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What is system-level meta data?
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Revision as of 05:06, 13 September 2006
What does the SRB do?
As the name implies the Storage Resource Broker, brokers storage resources (sorry, couldn't resist). It provides access, via a uniform API, to various types of data storage across local and wide-area networks, and maintains meta-data (data about the data) about each stored object (files). SRB, in conjunction with MCAT, provides a means for accessing data objects and resources through querying their attributes instead of knowing their physical names and/or locations.
The SDSC Storage Resource Broker (SRB) provides the abstraction mechanisms needed to implement data grids, digital libraries, and persistent archives for data sharing, data publication, and data preservation.
Many people, using only a subset of the features, find that using the SRB as global file system is its most compelling function. Users of multiple distributed computing systems find it to be an essential tool to easily and quickly access files from various locations. With the SRB's parallel I/O capabilities, the SRB will transfer files at least as quickly as any other mechanism, and usually faster.
What is zoneSRB? or How can I federate SRB systems?
ZoneSRB (or federated MCAT SRB) is the next generation of the SRB released as Version 3.0. It provides facilties for two or more independent SRB systems to interact with each other and allow for seamless access of data and metadata across these SRB systems. These systems are called the 'zones. More information about zoneSRB can be found at Fed MCAT.
What kinds of resources does the SRB support?
Storage resources can be directories in Unix file systems, directories in Windows file systems, archival storage systems such as HPSS (and, previously, UniTree and DMF), binary large objects stored in a DBMS (DB2, Oracle, Illustra), database SQL-queriable objects in DB2 or Oracle, and tape library systems. Tape systems can be combined with disk cache into Compound Resources, and the SRB can function as a complete basic archival storage system. SRB includes a set of tape I/O functions and an interface to the STK tape library system.
Is the SRB Open Source?
No, not exactly, although the full source code is readily available to academic organizations and government agencies. The normal distribution is via source. The client sources, that is the Scommands, client C library, inQ, and Jargon, are freely available via a BSD license. Interfaces on top of these, Matrix for example, are also readily available. For commercial applications, please contact the UCSD Technology Transfer & Intellectual Property Services at email@example.com. See Is_SRB_Open_Source for more information.
How does the SRB compare to commercial software?
As far as we know, there is no commercial product much like the SRB (except for the commercial version of the SRB, see below). The biggest difference between commercial software and research products like the SRB is the lack of a Quality Assurance testing group. But we do a lot of testing of new features, as do our collaborative sites, and we have recently developed some automatic testing scripts and systems. SRB is also a mature product as it has been in production use since 1997. In 2000, a government agency thoroughly examined the code and provided us with fixes (memory overruns, etc). The design is such that most problems are fail-safe, due the the client/server design, and cross-checks within our MCAT library and of the DMBS systems themselves. We build on the quality and robust-features of modern DBMSs.
Is there a commercial version?
Yes, General Atomics has certain exclusive commercial rights. See http://www.nirvanastorage.com. Nirvana Storage's SRB software split from SDSC SRB software in version 1.1.8 in 2001.
Since then SDSC has released multiple versions of the SRB software with substantial enhancements including Zones, Bulk Operations, improved administration/installation, stronger security, extended clients such as inQ, JARGON, MySRB, Matrix and Kepler, and extended metadata capabilities.
The SRB protocol used in the SDSC SRB system provides many new features and functionalities and differs from the protocol used by Nirvana.
How does the SRB relate to Grid technologies?
In many ways:
a) The SRB is a complete data Grid system in itself, and has been since SRB 1.0 in 1997. It operates, in production, as collections of client and server hosts distributed across local and/or wide-area networks, cooperating to provide transparent access to storage resources, data, and meta-data (data about data).
b) We are participating in many data grid research and development / production collaborations, including PPDG, GriPhyN, BaBar, CDL, NASA Information Power Grid and many more. The SRB is either used in production or is being evaluated across multiple projects at NSF, NASA, DOE, DOD, NIH, NLM, NARA, and the Library of Congress. See Projects
c) We support the Globus Grid Security Infrastructure (GSI) as an
optional method of authentication.
d) The SDSC Matrix workflow management system is a grid-based system and uses a Web Service Definition Language (WSDL) interface.
e) We plan to develop an OGSA-compliant SRB.
Is the SRB middle-ware?
Yes and no. It can be considered middle-ware like other grid technologies as it can be combined with higher level software, can interoperate with other grid components, and depends on other lower-level systems (archives, file systems, networks, a DBMS for the metadata catalog, etc). But unlike many other middle-ware components, SRB does not have to be combined with higher-level software to be utilized. With the various clients (Scommands, inQ, mySRB, etc), SRB is also a complete solution itself, a functional whole.
How secure is the SRB?
The SRB is quite secure. No computer system is perfectly secure, but the SRB provides a reasonable level of security while still providing convenience features and high performance. The Encrypt1 challenge/response is secure against network eavesdropping, while the use of user passwords is convenient and straight-forward for both users and administrators. Placing user passwords into files on host systems is a convenience, although if a host is compromised, those files could be read and the user's SRB identity assumed. GSI is also secure against network eavesdropping and somewhat less vulnerable against compromised hosts as only temporary delegation certificates are stored in files.
Generally, the SRB is as secure as the DBMS used to store the MCAT and the physical resources used to store the data. User identity is as secure as the client host system.
Since the SRB server runs as a non-root user, it does not present a vulnerability to the OS if compromised. This is a big advantage over software systems that need to be run as root.
Starting in April 2004, SRB releases include a paper describing how to run a secure SRB system: readme.dir/srb-security.html.
Starting with SRB 2.1 (late May, 2003), we provide a mechanism by which SRB data files can be encrypted for both network transmission and storage. This system provides security against network eavesdropping for the data objects exchanged via the SRB and also improves the security of the data objects as they reside on any of the various physical resources. This system was implemented to be efficient, although the encryption and decryption is always a compute-intensive operation and there will be some unavoidable performance penalty. See Secure Compressed Data for more information.
How fast is the SRB?
For transferring large files, SRB will normally be significantly faster than FTP, SCP, or NFS and the like, because of the SRB's parallel I/O capabilities (multiple threads each sending a data stream on the network). Sreplicate and Scp use parallel I/O for large-file data transfers by default, and you can use the -m option on Sput and Sget to select parallel I/O.
For small files, transfers can be a little slower due to the additional interaction with the MCAT (especially to a remote MCAT), but you can use Containers and/or Sbload (Bulk load) and Sbunload (Bulk unload) to greatly speed these. For more information see, the man pages and Containers questions in this FAQ. We are working toward enhancing Sget and Sput to do bulk operations to non-container files to speed them up too.
How was the SRB developed?
We were funded through a series of research/development proposals. After the initial version, we used the SRB as a basis for additional proposals and applied research projects. Because of this, the SRB is very customer driven, as we strive to meet the specific needs of current projects. Since the projects are similar in nature (at the SRB level), they often share a similar set of requirements, and we can usually leverage the development for one project to assist in other current and/or future projects. In this sense, the SRB provides a uniform data management fabric layer to build large applications.
How many people work on the SRB?
The SDSC SRB Team is currently about 11 people (depending how you count). We also encourage others to develop and share new features. We have integrated a number of capabilities developed outside the core group. We receive a lot of advice and suggestions from the community, both formally and not.
What support is provided?
We will freely provide answers and provide some limited support to help get sites up and running with the SRB. There is a srb-chat email list for SRB admins, developers and users to discuss questions, problems, and solutions (it includes an archive of previous posts). Our web site includes information on current bugs, future plans, current projects, etc. The SRB tar release contains many README files to explain installation and operation. Of course, many of our activities are collaborative funded projects which include specific development tasks and more extensive support.
What operating systems does the SRB run on?
SRB has been ported to a variety of Unix platforms including Linux, Mac OS X, AIX (ex. SP-2 machines), Solaris, SunOS, SGI Irix and to Windows. The Windows version of the Server cannot be configured with an MCAT (so it talks to one that is), but can store and retrieve data from the Windows file system. SRB is easily portable to Unix-type OSes.
What authentication mechanisms are available for SRB?
SRB supports three types of authentication: 1) A basic password-based authentication (now phased out), 2) password-based authentication in which the password is used in a challenge-response protocol so no plain-text password is sent on the network ("Encrypt1"), and 3) GSI authentication. Encrypt1 is a simple and secure stand-alone authentication system. In both password-based systems, user passwords are stored in the MCAT and users can record their passwords into their ~/.srb/.MdasAuth file to provide convenient and reasonably-secure access. GSI (Globus Grid Security Infrastructure) is convenient when using other Globus tools but requires users to acquire Certificates (i.e. a Public Key Infrastructure is needed). Previously we also supported SEA authentication (SDSC Encryption and Authentication system) but now GSI provides similar functionality.
What are the future plans for the SRB?
We'd like to see the use of the SRB continue to expand, and expect that it will. We will continue to add new features. We are currently participating in many collaborative projects under various funding agencies, and have every reason to believe that this will continue long term. See our plans for the near future in our [Bugzilla] system which we use to track bugs and pending features.
Where can I find more information about SRB and related systems?
We maintain a set of web-pages at http://www.sdsc.edu/srb where a lot information about the SRB is available. This FAQ also contains many links to additional information on specific topics. There are also many documents included with the release under the MCAT and readme.dir directories.
Some general information is also available in http://en.wikipedia.org/wiki/Storage_resource_broker.
What kind of query capabilibities are available?
In SRB, we have two types of metadata: "system" and "user-defined". "system" metadata are maintained by the SRB server and "user-defined" are maintained by users. We have well defined API's and utilities for querying both "system" and "user-defined" metadata.
How can I SRB-enable my application?
See How To SRB Enable for a list of options and links to additional information.
How does SRB compare with competing products?
The following is a list of products that compete with SRB in some manner, with a brief description of some differences. SRB is an integrated solution for distributed data management and distributed shared collections.
- AFS - SRB is more than a file system. SRB manages metadata, replication, parallel I/O, containers.
- Veritas - SRB is more than a backup system, it supports replicas, versions, and snapshots of files and containers.
- Oracle 10g IFS - SRB is more than a database system, it supports execution of SQL commands at remote databases.
- HPSS - SRB is more than an archive system, it integrates access across administrative domains and across heterogeneous storage systems.
- Avaki - SRB is more than a persistent object environment, it manages relational metadata.
- Globus toolkit - SRB is more than a set of services. SRB manages consistent state information in distributed environment.
Interfaces and Tools
What are the Scommands?
Scommands refers to a set of utility routines that can be used in a Unix shell or Windows DOS command shell and access data and meta data information from SRB and MCAT. For more information on Scommands see User_Environment. Scommands also have a set of man pages describing each of the commands. One first logs in via a Sinit, and can then do Sls, Scd, Sput, Sget, etc. For the full list see the Scommands Man pages .
What is inQ?
inQ is a graphical SRB client for Windows 98/Me/NT/2k/XP.
In a nutshell, inQ provides a familiar file-manager-like interface that SRB users can use to manage their data stored on SRB; actually it's more like a file-manager interface on steroids. inQ looks and acts a lot like Windows Explorer or Nautilus but also throws in features found in several web browsers like Internet Explorer or Netscape Navigator. It offers an easy way to manage metadata and access permissions, as well as a query builder capable of performing nested queries. It also throws in friendly, context-sensitive buttons that show you which actions can be performed on any given item in SRB.
What is MySRB?
MySRB is a web-based browse and search interface to the SRB. See the mySRB home page at http://www.sdsc.edu/srb/mySRB/mySRB.html for more information.
What APIs are available?
The most comprehensive programmatic API is the SRB C library which can be linked with any application program. We also have a pure Java client library, Jargon, which includes all the client function calls. Almost all of the C library calls can be accessed through our Python binding. Some sample programs for using the API can be found in the release under test/examples. Also see the API description at C_API and SRB User Manual
What is the srbBrowser?
The srbBrowser is a java-based graphical SRB client. It provides a subset of the functionality of inQ but can be used as a graphical client on Unix systems.
What is the mcatAdmin (Java Admin Tool) ?
mcatAdmin (also commonly called the Java Admin Tool) is a java-based graphical (GUI) srb-mcat Administration tool. It assists in the administration by making clear the available functions (like most GUIs) and presenting available values from which to choose. For example, when adding a new user, the existing domains are listed and the adminstrator clicks on the domain to use for the new user. And when modifying a user, one clicks on a domain and is given a list of the users in that domain to choose from. The GUI includes windows to create, display, and modify zones, users, resources, locations, domains, and other tokens. There are also command-line utilities that perform administrative functions.
What is Jargon (Java API)?
JARGON is a pure Java API for developing SRB (or other) datagrid interfaces. The API currently handles file I/O for local and SRB file systems and is easily extensible to other file systems. File handling with JARGON closely matches file handling in Sun's java.io API, a familiar API to most java programmers.
What is the SDSC Matrix?
SDSC Matrix is a data grid workflow management system. Matrix can be used to create, access and manage workflow process pipelines. Matrix internally uses the Data Grid Language, which can be used to describe, query and control process-flow pipelines.
The Matrix API can be used to define multiple SRB commands (and non-SRB grid services) as a single dataflow process and execute it on multiple servers. Matrix is available as a (SOAP/WSDL) web service. Matrix client programming for SRB is made very simple using a developer friendly Java API (less learning curve).
Does MCAT functionality vary from one client to another?
All functionalities are supported in the Scommand utilities for Unix/Linux/MacOSX and Windows. This is because we do all development on Unix clients and they get ported to other platforms. The MySRB provides a different perspective to metadata management but on a single-file level and collection level. It provides a good way of browsing and querying of metadata across collections, and also allows for ingesting, extracting, updating and deleting metadata and user annotations for single SRBobject or SRB collection. The inQ provides a unique capability where one can associate metadata to SRB objects and collections in an intuitive way and also query across collection and form (temporary) query-collections. This allows one to query based on attribute-metadata and then get a collection and slowly refine the query to drill down to a sub-collection that is of interest.
Hence, each client provides a unique way of handling metadata and their management. One of our goals is to provide uniform functionality across all client interfaces. But this requires a huge amount of programming which we are unable to dedicate at this time.
Is one client better than another for entering metadata?
The Scommands client is very good for entering metadata. As mentioned before one can use inQ or MySRB for entering/updating metadata of individual SRB object and SRB collection. But the Scommands provide for Bulk ingestion of metadata for multiple SRB objects possibly residing in more than one SRB collection.
For cutting and pasting, there are utilities in both MySRB and in Scommands for copying metadata from one SRBobject to another, from one SRB collection to another and from one SRB collection to an SRB object. This is different from cutting and pasting as it is done internal to the SRB and not at the user-GUI.
Is there a way to load attribute/value pairs from another application into the MCAT?
Yes. SRB allows one to bulk ingest metadata associated with one or more SRB objects. This is done by writing a metadata file in a particular format. Hence, if an application can generate a file in that format or one can write a wrapper which takes the application output and creates the file in the SRB metadataFile format then we can ingest the metadata attribute/value pairs. Actually, if you are doing this in Unix-based systems you can do that by writing simple scripts or by piping multiple applications together with the final pipe going to the SRB Scommand for ingesting metadata.
Also another unique way of associating metadata for SRB objects is to do automatic extraction INSIDE SRB and storing them in the MCAT. This is done by writing simple templates (basically rules) that allows one to identify the metadata values in the SRB object and then extracting them and storing them as attribute-value pairs in the MCAT. We have done this type of templates for multiple file formats including DICOM, FITS, email, NSFAwardAbstracts and HTML files. This can be launched through the MySRB or through the Scommands.
What is MCAT?
MCAT, or Meta data Catalog, is a meta data repository system implemented at SDSC to provide a mechanism for storing and querying system-level and domain-dependent meta data using a uniform interface. MCAT provides a resource and data object discovery mechanism that can be effectively used to identify and discover resources and data objects of interest using a combination of their characteristic attributes instead of their physical names and/or locations.
What is meta data?
Meta data is information about data.
What is system-level meta data?
MCAT considers five kinds of entities as primitive objects on which it keeps additional information. These are: data objects, resources, collections, users and methods. The system-level MCAT meta data items are these primitive objects and others derived from these.
Since there are primitive MCAT objects, are there other MCAT objects?
There are many derived MCAT objects. For example, MCAT, in the current release, supports notions of logical resources, compound resources, user groups, etc.
What is application-level meta data?
Application-level meta data are information about data objects that pertain to the non-systemic description of the data objects. Application-level meta data are characterized by information that is particular to the data for that application and are not generalizable across all data objects. For example, location, size, creation date information are systemic as they are available for every data object where as information about how the data object was created and what parameters were used in its creation may not be easily generalized across all data objects and hence form part of application-level meta data. Also, certain applications might have metadata specific to the data object such as FITS metadata used in Astronomy and DICOM metadata for medical images.
What is domain-dependent meta data?
Domain-dependent meta data is another name for application-level meta data.
Does SRB/MCAT support application-level meta data?
Yes, the SRB does support application-level meta data. There are two ways in which the SRB can support application-level meta data: First, as user-defined metadata and second as schema-extended metadata.
What databases can be used for installing MCAT?
MCAT can be installed on either Oracle, DB2, Sybase, Postgres, Informix, or MySQL 4. SQLServer, since it is so similar to Sybase, should be fairly straight-forward to implement too.
What do I need to run SRB?
As noted elsewhere, one can have many different setups of SRB. You can get the source code for any of these setups and build your SRB server or client as needed. SRB has been ported on to several platforms (see appropriate FAQ question) and we recommend that you use one of these. If you port to other platforms, we would be glad to include it in our subsequent releases. If you are setting up an MCAT-enabled SRB, you will require either an Oracle, DB2, Sybase, or Postgres database to which MCAT has been ported. We also recommend having a separate user-account called 'srb' (or any variant such as "ucsdsrb") which can be used for setting, administrating and running the system. Once you have the source for SRB and/or MCAT, separate readme files are included to take you through the build, setup and test process.
What are the hardware requirements (disk space, CPU speed, memory) for an SRB Server host?
The hard disk size depends upon how much storage you want to broker. The SRB software system itself requires only about 200 MBytes of storage. For MCAT-enabled servers, the DBMS will require additional space; on Linux, for example, the SRB with Postgres and ODBC take about 700 MB.
We normally recommend 1 to 6 TBytes, depending on the usage. We have specs for a system called the SRB Brick which costs around $15K for 6 TBytes (January, 2005).
As for CPU speeds, any Linux system with more than 1.5 GHz should be fine. Memory of 1/2 GB or 1 GB will be sufficient.
Which DB system should I use?
For a large and/or heavy-load instance of SRB, you will probably want to use a commercial DBMS like Oracle. It does have better performance, at least in many cases. It costs money though, and you really should have a DBA to manage it. We also have a project planned for the fall 2005 (with some UK folks) that would make use of some Oracle features (including some stored procedures) that will further enhance performance when using Oracle.
Postgresql works fine for initial testing (for "getting your feet wet"), and it works fine for light to moderate data loads. It is also relatively easy to install via our install.pl script. It is used in production for some projects (for example, SIOExplorer project which takes SRB ship-board for ocean surveys). Some Postgresql tuning is available via the 'install.pl vacuum' and 'install.pl index' commands (see install.pl for documentation).
For any DBMS system, the performance decreases as the size of the MCAT increases.
What is a data object (data set)?
In the terminology of SRB, a data object is a "stream-of-bytes" entity that can be uniquely identified. For example, a file in HPSS or Unix is a data object, or a LOB stored in a SRB Vault database is a data object. Importantly, note that a data object is not a set of data objects/files. Each data object in SRB is given a unique internal identifier by SRB. A data object is associated with a collection (see below). Previously, we used the term "data set" for this, but are phasing it out (as it was often confusing) and instead using "SRB data object".
Who is a registered SRB user?
SRB users are registered in the MCAT catalog and are given unique SRB ids. These identifiers are independent of the location or system ids, such as Unix ids.
What is a method?
In the terminology of SRB, a method is any executable piece of code that is registered in the MCAT catalog.
Methods can be defined to operate on data on the server before being returned to the client. This can be quite efficient in cases where the data object is being reduced by the method (for example, the method selects a subset of the data object based on inputs, such as metadata extractors (FITS, DICOM, etc)). Format converters, such as tiff2gif and tex2ps can also be useful SRB methods.
Who is SRBadmin?
SRBadmin is the person who creates and manages SRB and MCAT systems. A SRBadmin is also a registered SRB user who has additional privileges compared to normal users. A SRBadmin does NOT need to have "root" privilege.
What is a (data object) collection?
A collection is a logical name given to a set of data objects. All data objects stored in SRB/MCAT are stored in some collection. A collection can have sub-collections, and hence provides a hierarchical structure. As a simple analogy, a collection in SRB/MCAT can be equated to a directory in a Unix file system. But unlike a file system, a collection is not limited to a single device (or partition). A collection is logical but the data objects grouped under a collection can be stored in heterogeneous storage devices. There is one obvious restriction, the name given to a data object in a collection or sub-collection should be unique in that collection.
What is the SRB logical name space?
It is easy to think of SRB Collections as Unix directories (or Windows folders), but there is a fundamental difference. Each individual data object (file) in a collection can be stored on a different physical device. Unix directories and Windows folders use space from the physical device on which they reside, but SRB collections are part of a "logical name space" that exists in the MCAT and maps individual data objects (files) to physical files.
The logical name space is the set of names of collections (directories) and data objects (files) maintained by the SRB. Users see and interact with the logical name space, and the physical location is handled by the SRB system and administrators. The SRB system adds this logical name space on top of the physcial name space, and derives much of its power and functionality from that.
What is a resource?
In the terminology of SRB, a resource is a software/hardware system that provides the storage functionalities. The term is equivalent to "physical resource". For example, HPSS can be a resource, as can a Unix file system.
What is a physical SRB resource?
A physical SRB resource is a system that is capable of storing data objects and is accessible to the SRB (see [FAQ:What kinds of resources does the SRB support?]). It is registered in SRB with its physical characteristics such as its physical location, resource type, latency, and maximum file size.
What is a logical SRB resource?
A logical SRB resource is a SRB resource that is derived from physical SRB resources. A logical SRB resource might be derived with further constraints on a registered physical resource or by combining more than one physical resource as an entity. For example, if a physical resource 'A' is defined using a particular directory in a HPSS, a logical resource A-bar might be defined as a resource that restricts to a further sub-directory in 'A'.
What is a logical SRB resource set?
A 'logical SRB resource set' is kind of logical SRB resource. It is defined as a set of physical SRB resources. The aim is for this is to give a unique (logical) name to a set of resources and when SRB opens or writes a buffer to the logical resource it opens or writes to every resource in that set. A logical resource containing multiple physical resources can be treated as a 'single' resource when using it.
What is a compound SRB resource?
A compound resource allows the SRB to function as a complete (although basic) archival storage system (also known as an hierarchical storage system (HSM)). A compound resource may be configured to contain a pool of cache resources and a tape resource. When a user creates a file using a compound resource, the object created becomes a "compound object". The actual data of a "compound object" may reside on cache or tape or both. Unlike the SRB replica, a "compound object" always appears as a single object even though there may be multiple copies of the data. It is a simple hierarchical system where data migrate automatically between cache and tape. Data is always staged on cache automatically whenever it is accessed and migrates to tape by the system administrator when more cache space is needed. The cache and tape resources can be distributed across a WAN.
What is a user group?
A user group is a uniquely identifiable name given to a set of SRB registered users.
Who can form a user group?
Any set of mutually agreeable users can form a user group.
Who can register a user group?
SRBadmin has the authority to register user groups.
What is a domain?
A domain is a string used to identify a site or project. Users are uniquely identified by their usernames combined with their domain 'smith@npaci'. SRBadmin has the authority to create domains.
What are tokens?
Tokens are string items stored in the MCAT used as root items when creating other items (resources, etc). We have quite a few predefined tokens. SRBadmin has the authority to create tokens.
What is a replicated data object?
In SRB, one can make copies of a data object and store the copies in different locations. But, all these copies in SRB are considered to be identifiable by the same identifier. That is, each copy is considered to be equivalent to each other.
How can one read a replicated data object?
When a user reads a replicated data object, SRB cycles through all the copies of the data object and reads the one that is accessible at that time. It uses a simple replica identificatoin mechanism to order this list of replicated data objects.
How can one create a replicated data object?
There are three ways of creating a replicated data object. In the first method, which can be viewed as asynchronous replication, one can create a data object (using Sput Scommand or srbObjCreate API), and then replicate the data object using the Sreplicate Scommand or the srbObjReplicate API. In the second method, which can be viewed as synchronous replication, one can define a 'logical resource set' as a set of resources and then create a data object in that logical resource set (using Sput Scommand or srbObjCreate API). SRB automatically replicates the data object as it gets written.
One can also off-line create two data objects separately in a physical resource and then register them as replicas of each other. This is called out-of-band replication. SRB provides the means to replicate collections of data objects recursively.
Also see "Replicated Data Management user SRB" (GGF-4, February, 2002) at http://www.sdsc.edu//srb/Pubs/SRBReplication.ppt.
What is a Container?
A Container is a way to put together a lot of small files into one larger file to improve performance. This works very well with resources that include tapes (such as HPSS). The whole container is retrieved from tape, cached on SRB disk, and then multiple files can be quickly read and written on the container copy on disk. The SRB handles the book-keeping for the container.
How do Containers work?
The SRB container is a like a tarball in the sense that it stores multiple files as a one single file. It grows the container on the fly by adding new files as they are ingested into the container. Hence, unlike a tarball, the container can be grown as needed. Also, unlike a tarball, users can read individual files without downloading the container on to their desktops.
The SRB keeps all the information about how the container is laid out in its Metadata Catalog (MCAT) and uses it when retrieving individual files. One can also modify and delete files in a container as though they are doing these operations on a normal file and the SRB takes care of the operation.
To answer a related question, the container is not "made" on the desktop and then loaded into the SRB. Instead it is constructed in situ on the resource. But what happens is that containers are normally assigned a logical resource which has two physical components: an archive resource such as the HPSS or roadnet-sam, and a cache resource such as a unix file system (eg. roadnet-unix). All the construction, file access and modifications are done on the cache resource and the storage of a full container or a non-needed container is done on the archive resource.
Hence, the archive sees a single file and the construction is done before getting into the archive on the cache resource (not on the users desktop) which is also a resource controlled by the SRB.
Containers grow in size and are pinched off into physical pieces by the SRB so that a container might look really long, but are actually multiple files of smaller sizes. Normally we recommend these pinching off to be around 100 MBytes or 200 MBytes but then can be in the GB range also. This is akin to blocks in a tape system.
What this means is that the user sees one container where they "put" in their data, but like a goods-train, the container is physically divided. Obviously individual files are much smaller than the container size. To give an example, in one of our collections, we have containers of size around 50 MBytes, storing files of sizes 2 MBytes each. Each container stores about 25 files in its physical blocks.
Does Sget work properly for files that are in containers?
Yes, Sget works fine for files in containers. The MCAT stores all the file offsets for each file in a container, and Sget will download just the portion of the container that has the file you are trying to download. Since Sget (currently) doesn't support any bulk operations it's still slow trying to download a lot of small files.
How do you discover the container information?
If you're on a windows machine InQ is the easiest, the file details show the container information. In Scommands, SgetD on a file prints container_name and the respective container (if any) that the file is contained in.
Once I know which container a file is in, what is the most efficient way to download the data?
If you just need a few small files, then running Sget on each will be the quickest. If you want all or most of the container, and you know the container you want to download, then simply running 'Sbunload <container>' will be much faster.
Who can register SRB users?
SRBadmin can add new users to the MCAT catalog.
Who can register physical or logical resources?
SRBadmin has the authority and the required privileged utilities to register physical and logical resources.
How does SRB provide access to remote storage systems?
SRB provides access to remote storage systems through a proxy mechanism. When one stores a data object under SRB, the data object is stored and accessed by SRB acting as a proxy for the user. Because of this mechanism, a user can store data objects on remote storage systems without having personal accounts at these site. In this mode, SRB acts as a 'system privileged proxy' user. The above proxy mode also allows for SRB to SRB authentication enabling servers to access files that are under the control of another SRB server.
Can multiple SRB servers be federated?
Yes. SRB servers can communicate to other servers and can form a federation. More than one federation can also exist with one SRB federation being unaware of another. A user can access data objects stored under any SRB in the federation provided the user has proper permissions.
In 3.0 we released a Federated MCAT capability, where complete MCAT-enabled SRB systems can be integrated with other SRB federations. Each MCAT member of such a federation is called an SRB Zone.
How does one SRB know about another SRB?
A SRB server knows about another SRB through the MCAT. When the SRBAdmin creates a location, a SRB host is specified. When the SRBAdmin ingests a resource at a location, that resource is associated with that SRB host.
What are the different setup configurations that I can have at my site?
First, there are three basic configurations for the SRB/MCAT system:
(1) client-only, (2) server without MCAT and (3) server with MCAT.
In the simplest configuration, one can use the SRB client components (client utilities, GUI applications, and libraries) at a site and use SRB servers running at remote sites or hosts. A SRB client can connect to a specific (possibly remote) SRB server and access data objects that are under the control of that server and/or other servers in the federation. With the client-only setup one cannot access any data object at the local site through SRB. In the second setup, a site can have a SRB server running locally but without any MCAT service. In this setup, the local SRB server can provide access to local resources and contacts another SRB server that has MCAT service for retrieving the meta data about data objects. In the third configuration, one can have a SRB server and a MCAT database running locally. Any client can talk to any SRB server and need not necessarily talk to a local or 'nearest' server.
Is MCAT needed to run SRB?
Yes, an MCAT is needed but you do not need to install one yourself. Many sites use the SDSC MCAT-enabled SRB to support their SRB system.
Where can I get SRB?
Source code and related material for SRB and MCAT can be obtained from the web-site at http://www.sdsc.edu/srb. The tar files are PGP encrypted and one can get the passwords for decrypting them by sending email to firstname.lastname@example.org.
What is a SRB Vault?
SRB vault is a data repository system that SRB can maintain in any of the storage systems that it can access. For example, the SRB runningat sdsc (host: srb.sdsc.edu) runs a SRB vault in its Unix file system, and another SRB running at sdsc (host: hpss47.sdsc.edu) runs SRB vaults in HPSS, a unix file system and a DB2 database. SRB vaults provide a convenient storage area for storing data objects. A data object stored in a SRB vault is stored as a SRB-written object and its access is controlled through the MCAT catalog. This is different to legacy data objects that can be accessed by SRB but which are still owned by previous owners of the data. One can define SRB vaults in any storage device that can be accessed by a SRB server. In thecase of file systems such as Unix and HPSS, a separate directory is used for the purpose, and in case of databases such as Oracle, DB2 orIllustra, a system-defined table with LOB-space is used for the purpose.
What is a SRB Space?
SRB space is a union of all SRB Vaults that can be accessed by a system of SRB servers. Users registered in the system can store, retrieve and modify data objects (provided owners of the data objects grant appropriate permits) in this space. Hence, one can visualize SRB space as a logical storage volume that is distributed and heterogeneous.
What are the various data object interfaces supported by SRB?
The SRB supports four types of interfaces. The first type is a stream interface. It allows Unix file operations such as open, close, read, write and seek on SRB data objects. The second is an object-level interface. It provides means to create, modify and destroy collections of objects, move, copy and replicate objects, and apply user-defined proxy operations on objectsto obtain a new type of the object. The third type is a discovery-level interface for obtaining meta data information about data objects (eg., replication information, ownership, access, location, type information, etc), resources and users. These operations accessthe information located in MCAT catalog. Finally, SRB provides an interface for modifying the data about data objects in SRB, and for performing access control and auditing on various SRB objects.
How do I backup SRB space, both SRB data and MCAT metadata?
It is a good idea to backup the MCAT database daily. If your MCAT DBMS (Oracle, DB2, etc) can do hot backups, then you can do it when the system is being used. Otherwise, you will need to stop the SRB (killsrb), do the cold backup and then restart the SRB.
As for the files stored under the SRB, one can do it in multiple ways: The first and easist is to backup the storage resource directory (for example, the SRBVault directory), as an incremental backup. Depending upon your system, you can do it on the fly or during PMs. Weekly PMs will be helpful.
A second startegy is to make sure that there are replicated copies of the file in two distributed storage systems which hopefully don't share any hardware and are geographically separated. This can be done either under user-control (replicate only those that are needed) or under srbAdmin control (possible with 3.0.2 release soon) which will replicate all files that are modified to a particular backup resource.
A third strategy, is to use the zoneSRB is to run a backupZone at a remote site and back up to this zone from your zone. We are testing and finalizing some protocols for doing this.
What ports does the SRB use? What ports do I need to open in a firewall to run the SRB?
The firewall needs to open some ports on the server side, and possibly on the client side too.
On the SRB server server-side, you must open the port that the srbMaster is listening on, plus a set of 100 or so configurable data ports (described below).
The srbMaster listens on the port defined in srb.h or specified in srbPort environment variable (often set in the runsrb script). By default, srb.h has DefaultPort "5544" but this can be changed via the configure --enable-srbport=value option. Regardless of the DefaultPort value, the srbMaster will listen on the port specified in the srbPort environment variable value if it is defined. You can edit the runsrb script to change this.
(The clients also need to know the port number to connect to. For the Scommands they will default to the value in srb.h or will use the number specified in the srbPort line in each user's ~/.MdasEnv file.)
To configure a specific range of ports for the servers, include '--enable-commports' on the configure line. Without this, the srbServers will use arbitrary ports.
By default, the configurable ports are 20000 to 20199 (see mk/mk.config COMM_PORT_NUM_START and COMM_PORT_NUM_COUNT). So './confiugre --enable-commports' will restrict the servers to using ports 20000 to 20199 (plus the DefaultPort). You can change the start and number of the ports via configure options --enable-commstart and --enable-commnum, for example: ./configure --enable-commports --enable-commstart=21000 --enable-commnum=200
Based on our experience, we recommend using at least 100 ports, but you may need more or possibly fewer. It depends on how many transfers (especially parallel transfers), you will have going at the same time. There's a MaxThread parameter in runsrb that specifies how many threads to use; 4 is default, but you may wish to increase that. Each of these threads uses a port, so each parallel transfer could take 4 (or MaxThread) ports. If the servers run out of ports, the later transfers will fail. So it's a trade-off. If you don't set commnum high enough, and you get quite a few transfers going at the same time, some of them could fail.
On the SRB client side, if you use the Sput or Sget -m option (server initiated connection for parallel I/O), the client's firewall needs to open at least 16 configurable ports. These are the same ports as the server uses, i.e. 20000 to 20199 if just --enable-commports is used. As with the server, the port range can be modified, for example: ./configure --enable-commports --enable-commstart=21000 --enable-commnum=16
But starting with 3.1.1, users can now use the -M option (client initiated connection for parallel I/O) which does not require the opening of ports on the client side.
The commports are used for data transfer and are also normally used for non-data connections too. If the server system (the srbMaster server) is prespawning server processes (PRE_SPAWN_CNT is greater than 0 in runsrb, which is normally the case), then the server will use one of these ports for its communication connection. The client will connect to the srbMaster on the defaultPort (5544 or whatever) and then will be told which port to connect back to for the particular pre-spawned server that has been assigned.
Does SRB exploit any specific interfaces to HPSS to optimize performance?
Yes, the SRB uses both the sequential POSIX like interface as well as the parallel mover interface of HPSS for data movement. We have a set of SRB API's for both types of interfaces. In addition, all our data movement utilities have a switch that allows users to choose between these two modes.
What kind of ingest rates can SRB get?
In terms of number of files per second, for files stored in HPSS, it is limited by the ingestion rate of HPSS (we are still using the ENCINA based HPSS). The SRB bulk load mechanism can do 30-50 files per second.
For I/O rate, it pretty much depends on the hardware and network. We can get up to 50 Mb/sec with 3-4 mover threads while the rate from HSI is about 30-40 % higher because data does not have to go through any SRB server.
How well does SRB handle packaging small data packets into "bundles", and store?
Very well. SRB can do bulk loads with or without containers (our term for "bundles"). Without using containers, a bulk load packs a large number of small files and ships them all at once to the server. The server then unpacks it into small files. With the use of containers, small files are packed into a container and the server saves the container as a single file. This use of containers is very simple and transparent to users. This is the recommended way of storing small files in HPSS.
What are the limitations of SRB, i.e 2TB of data, # of data entries?
There are practically no limits due to the SRB itself (address space of 64 bits). The underlying resources (e.g., file system) may have limits. At SDSC, SRB is managing 126 million files and 830 TB as of 9/18/06
SRB allows very long file names. However, the maximum length of a SRB file name is fixed and depends on the SRB version you are using.
The maximum file size of a single SRB file depends on the underlying storage resource where the file would be stored.
The number of files you can store depends on the database you use to support MCAT. Each file you store in SRB results in more tuples (rows) in MCAT database. Each database vendor will have their own limitation on the number of tuples (rows) that can be supported (usually this is a very very large number).
Who can register data objects?
Any SRB user can register data objects. When a user creates a data object in SRB, the data object is automatically registered in SRB. A user can also register legacy data objects that they own and created outside SRB using the Sregister Scommand or the srbRegisterDataSet API.
Who can create data object collections?
A collection is always created as a sub-collection under an existing collection (SRB/MCAT when it is initialized starts with a root level collection). Any SRB user can create data set sub-collections provided they have permission to create sub-collections under the pertaining collection.
Who can use SRB?
To use SRB one needs to be a registered SRB user. One can register themselves by sending email to a SRBadmin. If there is a local SRB system administrator then requests should be to them, otherwise applications can be made to email@example.com. There is one mechanism, called ticket-based access, that allows unregistered users to access (read only) data objects stored under SRB's control. Owners of data objects can issue tickets on their data objects that can allow everyone to access the data objects. Separate APIs have been developed that can be used by unregistered users.
How does SRB deal with unregistered or anonymous users?
SRB provides access to unregistered users using a second kind of proxy mechanism. In this mode, SRB acts as a 'ticket user proxy' and facilitates access to data objects through the ticket mechanism.
What are the types of access control provided by SRB/MCAT?
SRB supports two types of access control. The first type is similar to Unix-type access control. In this type, the owner can provide read, write and all access to other users or user groups at the level of individual data objects and collections. Unlike Unix, one can control access to as many users as needed and as many groups as needed. The second type of access control is controlled through tickets. Tickets are issued by owners of a data object (or collection) to other users, groups and everyone. One can use these tickets to access data objects that they control. A ticket user need not be a registered SRB user. There are APIs and Scommands that can permit non-registered users to access ticketed data objects.
What are the different modes of access control, supported by SRB?
SRB supports the following modes: read(r), write(w), all(a), annotate(t), and none(n). Read and write permissions refer to the data, annotate to metadata, and all means ownership. A user with 'all' permissions can change the permissions.
What is the 'all' mode of access control?
The 'all' mode provides a complete access control to a user. A user with this permission can not only read and write the data object (or collection) but also grant and revoke access permits for others for the object. The user can also issue tickets on the data object. At the collection-level, the mode grants sub-collection creation permission to the holder.
Can only one user have 'all' permission on a data object?
No. Any number of users can have 'all' permission on a data object. When a data object is registered, the registrar is considered to be the owner of the data object and is given the 'all' permission for access. Subsequently, the owner can grant this permission to other users and these users can grant the same to others.
Since data objects can be stored in remote storage devices, should I remember the path names or location information of my data object?
No. SRB along with MCAT relieves you of the necessity to remember physical locational details for your data object. For each data object, MCAT stores all the physical details abouts its location (and indeed about locations, since a data object can be replicated) and details about access mechanisms that are needed to open that location.
How does one use resources? When are they specified?
You don't need to specify a resource when getting or accessing an SRB file, as the SRB system will determine the best resource to use. For example, if you Sget a file that is replicated on both a disk resource and a tape resource, the SRB server will read the file on disk.
When you store a file, you need to inform the SRB system which resource you want to use, as they have different characteristics for different uses. For example, if you know a file is for long-term storage, you may want to store it to an archival resource (to go to tape) rather than to a disk cache.
For the Scommands, you can set a default resource in your ~/.srb/.MdasEnv file. Then, when you Sput a file, it will be stored on your default resource unless you use the Sput option to specify a different resource.
Your local SRB administrator can help you with using the appropriate resources for your SRB system.
How do I know in which collection to store my data?
Each SRB-registered user is started with a 'home' collection. They are given read, write and create-sub collection and grant permission to that collection. But, SRB/MCAT can also maintain project-level collections that can be shared by users and groups. Hence, one can store their data objects either in their home-collection hierarchy or in a project collection hierarchy in which thet have appropriate access permissions.
How useful are collections?
Collections provide a logical grouping mechaism. Assume that you have several data objects coming out of an experiment and further assume that few of the data objects are very large containing raw data (or image) generated by the experiment and a few other data objects are small and possibly containing some meta data information about the experiment. One can logically group these data in a collection (possibly by its experiment name and timestamp) and place the collection with other ones of similar kind. Physically, the large data objects may be stored in archival storage systems or in a large-scale disk system closer to where you are planning to perform some studies on the data (ex. a disk attached to a T3E system) and the smaller data objects may be stored in a local file or database system. By logically bundling the data objects in one collection, one has a single point of access for the experimental data.
Should my data always be in a collection?
Yes. Every data object under SRB/MCAT is associated with a collection.
Can I have the same data object in more than one collection?
Yes, the SRB does support soft-linking of data objects across collections.
How do I identify a data object?
In the simplest case, a user can access a data object by knowing its name and its collection name. The SRB/MCAT system also provides a rich discovery system for identifying data objects. They provide a query-based capability to identify dataets using srbObjOpen() and srbGetDataDirInfo() APIs. In these two calls, the objID parameter provides the means to provide the characteristics for the data object(s) of interest. The objId parameter can be a data object name or can be a set of attribute-condition-value triplets. These triplets are viewed as providing a conjunctive characteristic that defines the data object of interest. For example one can provide in objId a string of the form "&DTYPE='C code' &DTIME>'1998-01-26-10.00.00' &DCOMMENTS like '%test%'" will get information about a C program that was created after 10 AM on January 26, 1998 and has been commented as test.
What is the srbObjOpen() API?
The srbObjOpen() API allows one to open a data object for further operation, such as read, write, seek, etc.
What is the srbGetDataDirInfo() API?
The srbGetDataDirInfo() API allows one to access information about data objects, stored in the MCAT catalog.
How do I know what are the available resources that I can use?
The Scommand called SgetR provides an easy means of finding the resources that are accessible in your SRB system.
How do I get information about a data object?
Scommands provide a few ways of getting this information. Using SgetD, Sls and using SgetU and SgetR with appropriate flags, one can access meta information about data objects. See What are the Scommands?
What are tickets? How can one issue them? use them?
The ticket system is a mechanism to control access to data objects. Tickets can be issued on a data object by a SRB user who has 'all' mode of access permission. SRB createsa ticket (which is an ASCII string) and associates withthe concerned data object (or collection). The issuer can attach someconditions on the use of the ticket. One can control the user base of the ticket by giving a list of user names and/or user-group names. One can issue a ticket to all users (both registered and un-registered SRB users) using a special user-name called 'ticket-user' (the APIs do it automatically if no user is mentioned). If one wants to allow access to only SRB registered users, then issuing a ticket to 'public' would serve the purpose. One can provide a begin and end date-time for the validity of the ticket. One can also provide a maximum count (which can be infinity, denotedby -1) for using the ticket. One can issue a ticket to a single data object or to a collection or to a recursive collection (i.e., collection and sub-collections ad infinitum). When a ticket is used, for a data object SRB/MCAT checks whether the issuer of the ticket still owns the data object before providing access to the data object. If a ticket issuer no longer has 'all' access permission at the time when the ticket is used, the data object access is denied. Note that if more than one data object is associated with a ticket and/or more than one user is allowed to use a ticket, the count of usage is at the ticket-level and not at per user or per data object level.
Can I issue ticket only for data objects?
Tickets are associated with data objects. Even though one can issue a ticket to collections or recursively to collections and sub-collections underneath collections, the tickets are still associated with data objects in those collections.
If a ticket is issued for a collection will that allow access to all data sets in that collection.
No. A ticket issued on a collection allows access ONLY to data objects in that collection for which the issuer has 'all' permission. Other data objects that belong to others are not accessible using that ticket. The same logic applies when tickets are issued for recursive collections.
Can I issue a ticket for a 'future' data object.
No and Yes. A ticket issued to a data object requires that the data object be registered at the time of issue. But, a ticket issued on a collection can allow acess to data objects that are created in the future but for which the issuer has 'all' access permission.
What is the difference between backup and replication?
A SRB file can be backedup or replicated in any number of resources. This improves data reliability and data access times. A backup-file is similar to any other replica of SRB file. The only difference comes from the operation used to create this replica.
During Backup of a SRB file on a given resource, the system checks if the target resource already has the latest copy of the file (uses the MCAT system metadata about the file). If the resource has the latest copy, no movement of data is made. If not, a new backup copy of the data is created on the specified resource. The advantage of the Backup is that no movement of data is made if the latest copy already exists in the backup-resource.
On the other hand, 'Replication' of SRB file does not check if such a replica already exists. The System creates a new replica of the file in the specified resource (even if there is another latest copy/replica in the specified target resource).
When a SRB File is accessed, the SRB system automaticlaly picks up the suitable replica (based on certain heuristics). Even a back-up file could be choosen (if it is the only copy or the fastest copy). This default behavior (of the DGMS choosing the replica) could be over ridden by exactly specifying the replica needed.