Introduction to SRM. Riccardo Zappi 1

Transcription

1 Introduction to SRM Grid Storage Resource Manager Riccardo Zappi 1 1 INFN-CNAF, National Center of INFN (National Institute for Nuclear Physic) for Research and Development into the field of Information Technologies SRM School, 2009 Bologna, Italy Data Management 1

2 Outline 1 Storage Element Storage services 2 GridFTP Service GridFTP Service 3 Genesis of SRM Genesis 4 File naming File naming in Grid Mapping services 5 SRM Service SRM service: main concepts Storage Area and Storage Component The Storage Resource Manager Interface Specification v2.2 6 Data access pattern Read a file Write a file 7 Conclusion Some SRM Service implementation

3 Outline 1 Storage Element Storage services 2 GridFTP Service GridFTP Service 3 Genesis of SRM Genesis 4 File naming File naming in Grid Mapping services 5 SRM Service SRM service: main concepts Storage Area and Storage Component The Storage Resource Manager Interface Specification v2.2 6 Data access pattern Read a file Write a file 7 Conclusion Some SRM Service implementation

4 Storage services Storage Resource All data is ultimately stored on a data storage resource (memory stick to a multi-petabyte tape silo) Different storage resources offer different levels of Quality of Service (QoS) The storage hardware will typically be controlled by software Definition The storage resource is the combination of the storage hardware and the controlling software (eg. file system) Data Management 4

5 Storage services Storage Element Storage Element (SE) A Storage Element (SE) is a Grid service that allows Grid users to store and manage files together with the space assigned to them. To make the storage available in the data architecture, the storage resource is wrapped by storage services Three categories of interfaces: 1 Data Access 2 Data Transfer 3 Storage Management Data Management 5

6 Storage services Storage Element Storage Element (SE) A Storage Element (SE) is a Grid service that allows Grid users to store and manage files together with the space assigned to them. To make the storage available in the data architecture, the storage resource is wrapped by storage services Three categories of interfaces: 1 Data Access 2 Data Transfer 3 Storage Management Data Management 5

7 Storage services Storage Element Storage Element (SE) A Storage Element (SE) is a Grid service that allows Grid users to store and manage files together with the space assigned to them. To make the storage available in the data architecture, the storage resource is wrapped by storage services Three categories of interfaces: 1 Data Access In theory: ByteIO, DAI In practise: rfio, dcap, file 2 Data Transfer 3 Storage Management Data Management 5

8 Storage services Storage Element Storage Element (SE) A Storage Element (SE) is a Grid service that allows Grid users to store and manage files together with the space assigned to them. To make the storage available in the data architecture, the storage resource is wrapped by storage services Three categories of interfaces: 1 Data Access In theory: ByteIO, DAI In practise: rfio, dcap, file 2 Data Transfer 3 Storage Management Data Management 5

9 Storage services Storage Element Storage Element (SE) A Storage Element (SE) is a Grid service that allows Grid users to store and manage files together with the space assigned to them. To make the storage available in the data architecture, the storage resource is wrapped by storage services Three categories of interfaces: 1 Data Access : rfio, dcap, file 2 Data Transfer 3 Storage Management Data Management 5

10 Storage services Storage Element Storage Element (SE) A Storage Element (SE) is a Grid service that allows Grid users to store and manage files together with the space assigned to them. To make the storage available in the data architecture, the storage resource is wrapped by storage services Three categories of interfaces: 1 Data Access : rfio, dcap, file 2 Data Transfer In theory: OGSA-DMI In practise: GridFTP 3 Storage Management Data Management 5

11 Storage services Storage Element Storage Element (SE) A Storage Element (SE) is a Grid service that allows Grid users to store and manage files together with the space assigned to them. To make the storage available in the data architecture, the storage resource is wrapped by storage services Three categories of interfaces: 1 Data Access : rfio, dcap, file 2 Data Transfer In theory: OGSA-DMI In practise: GridFTP 3 Storage Management Data Management 5

12 Storage services Storage Element Storage Element (SE) A Storage Element (SE) is a Grid service that allows Grid users to store and manage files together with the space assigned to them. To make the storage available in the data architecture, the storage resource is wrapped by storage services Three categories of interfaces: 1 Data Access : rfio, dcap, file 2 Data Transfer : GridFTP 3 Storage Management Data Management 5

13 Storage services Storage Element Storage Element (SE) A Storage Element (SE) is a Grid service that allows Grid users to store and manage files together with the space assigned to them. To make the storage available in the data architecture, the storage resource is wrapped by storage services Three categories of interfaces: 1 Data Access : rfio, dcap, file 2 Data Transfer : GridFTP 3 Storage Management In theory: SRM In practise: SRM Data Management 5

14 Storage services Storage Element Storage Element (SE) A Storage Element (SE) is a Grid service that allows Grid users to store and manage files together with the space assigned to them. To make the storage available in the data architecture, the storage resource is wrapped by storage services Three categories of interfaces: 1 Data Access : rfio, dcap, file 2 Data Transfer : GridFTP 3 Storage Management : SRM In theory: SRM In practise: SRM Data Management 5

15 Storage services Storage Element Storage Element (SE) A Storage Element (SE) is a Grid service that allows Grid users to store and manage files together with the space assigned to them. To make the storage available in the data architecture, the storage resource is wrapped by storage services Three categories of interfaces: 1 Data Access : rfio, dcap, file 2 Data Transfer : GridFTP 3 Storage Management : SRM Data Management 5

16 Outline 1 Storage Element Storage services 2 GridFTP Service GridFTP Service 3 Genesis of SRM Genesis 4 File naming File naming in Grid Mapping services 5 SRM Service SRM service: main concepts Storage Area and Storage Component The Storage Resource Manager Interface Specification v2.2 6 Data access pattern Read a file Write a file 7 Conclusion Some SRM Service implementation

17 GridFTP Service What is GridFTP? GridFTP - File Transfer Protocol in Grid Computing Networks. high-performance secure reliable data transfer protocol optimized for high-bandwidth wide-area Data Management 7

18 GridFTP Service GridFTP: The Protocol GridFTP protocol extends the FTP standard with: Strong authentication, encryption via GSI on both control (command) and data channels Third-party transfers: C can initiate a transfer from A to B. Multiple data channels for parallel transfers Striped data transfers Partial file transfers Tunable network and I/O parameters Data Management 8

19 GridFTP Service GridFTP: The Protocol definition and GridFTP enabled servers A protocol GFD.47, GridFTP v2 Protocol Description GFD.20, GridFTP: Protocol Extensions to FTP for the Grid Multiple independent implementation can interoperate The Globus Toolkit supplies a reference implementation of : Server, Client tools (globus-url-copy) and Development Libraries Another client developed and supported at NCSA: UberFTP Data Management 9

20 GridFTP Service GridFTP channels Two channels protocol like FTP: Control Channel Communication link (TCP) over which commands and responses flow Low bandwidth; encrypted and integrity protected by default Data Channel Communication link(s) over which the actual data of interest flows High Bandwidth; authenticated by default; encryption and integrity protection optional Data Management 10

21 Outline 1 Storage Element Storage services 2 GridFTP Service GridFTP Service 3 Genesis of SRM Genesis 4 File naming File naming in Grid Mapping services 5 SRM Service SRM service: main concepts Storage Area and Storage Component The Storage Resource Manager Interface Specification v2.2 6 Data access pattern Read a file Write a file 7 Conclusion Some SRM Service implementation

22 Genesis Genesis from hierarchical storage Originally SRM designed to handle Tape/Disk-cache scenario: Staging of files A request for a file arrives If it is in cache it is returned right away Otherwise it is first fetched from tapes, copied to disk and then returned. The system takes care of consistency between cache and tapes. Needed to offset latency due to robotic arm switching tapes. Data Management 12

23 Genesis Genesis: Disk cache The presence of cache area introduces the concept of file type: Volatile files get written in cache and the system then removes them automatically after a lifetime expires Permanent the files that get into cache are not removed automatically by the system Durable files do have a lifetime that may expire but the system does not remove them and instead sends an notification to the user Data Management 13

24 Genesis Genesis: File Name abstraction The cache area also introduces a partition of file namespace: Tape must store files: there have to be names that uniquely identify the file in tape! The cache area must serve files. It may return a path to fetch the file on disk that is different from the name that allows to uniquely identify the file in tape. SRM reflects this distinction in the concept of SURLs and TURLs. SURL : Identify a grid file in SRM storage. TURL : Identify a URL to fetch the grid file. Data Management 14

25 Genesis Asynchronous requests File staging introduces the concept of asynchronous calls to get or put a file: SRM request issued to get a file Server replies immediately without waiting for staging to complete. Server returns a Request Token which the client uses to periodically poll the request s status. Data Management 15

26 Genesis Space Management Big issue of not running out of space during a large file transfer. System used by the HEP community to store/manage huge amounts of data from LHC. SRM introduced space management and reservation interface. Data Management 16

27 Outline 1 Storage Element Storage services 2 GridFTP Service GridFTP Service 3 Genesis of SRM Genesis 4 File naming File naming in Grid Mapping services 5 SRM Service SRM service: main concepts Storage Area and Storage Component The Storage Resource Manager Interface Specification v2.2 6 Data access pattern Read a file Write a file 7 Conclusion Some SRM Service implementation

28 File naming in Grid Data Resource and File Files in the Grid can be referred by different names: Logical File Name (LFN) : An alias created by a user to refer to some item of data Grid Unique IDentifier (GUID) : A non-human-readable unique identifier for an item of data Site URL (SURL) : The location of an actual piece of data on a storage system Transport URL (TURL) : Temporary locator of a replica + access protocol understood by a SE Data Management 18

29 File naming in Grid Data Resource and File Files in the Grid can be referred by different names: Logical File Name (LFN) : An alias created by a user to refer to some item of data Grid Unique IDentifier (GUID) : A non-human-readable unique identifier for an item of data Site URL (SURL) : The location of an actual piece of data on a storage system Transport URL (TURL) : Temporary locator of a replica + access protocol understood by a SE Data Management 18

30 File naming in Grid Data Resource and File Files in the Grid can be referred by different names: Logical File Name (LFN) : An alias created by a user to refer to some item of data lfn:cms/ /run2/track1 Grid Unique IDentifier (GUID) : A non-human-readable unique identifier for an item of data Site URL (SURL) : The location of an actual piece of data on a storage system Transport URL (TURL) : Temporary locator of a replica + access protocol understood by a SE Data Management 18

31 File naming in Grid Data Resource and File Files in the Grid can be referred by different names: Logical File Name (LFN) : An alias created by a user to refer to some item of data lfn:cms/ /run2/track1 Grid Unique IDentifier (GUID) : A non-human-readable unique identifier for an item of data Site URL (SURL) : The location of an actual piece of data on a storage system Transport URL (TURL) : Temporary locator of a replica + access protocol understood by a SE Data Management 18

32 File naming in Grid Data Resource and File Files in the Grid can be referred by different names: Logical File Name (LFN) : An alias created by a user to refer to some item of data lfn:cms/ /run2/track1 Grid Unique IDentifier (GUID) : A non-human-readable unique identifier for an item of data guid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6 Site URL (SURL) : The location of an actual piece of data on a storage system Transport URL (TURL) : Temporary locator of a replica + access protocol understood by a SE Data Management 18

33 File naming in Grid Data Resource and File Files in the Grid can be referred by different names: Logical File Name (LFN) : An alias created by a user to refer to some item of data lfn:cms/ /run2/track1 Grid Unique IDentifier (GUID) : A non-human-readable unique identifier for an item of data guid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6 Site URL (SURL) : The location of an actual piece of data on a storage system Transport URL (TURL) : Temporary locator of a replica + access protocol understood by a SE Data Management 18

34 File naming in Grid Data Resource and File Files in the Grid can be referred by different names: Logical File Name (LFN) : An alias created by a user to refer to some item of data lfn:cms/ /run2/track1 Grid Unique IDentifier (GUID) : A non-human-readable unique identifier for an item of data guid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6 Site URL (SURL) : The location of an actual piece of data on a storage system srm://storm.cnaf.infn.it:8444/infngrid/test.txt Transport URL (TURL) : Temporary locator of a replica + access protocol understood by a SE Data Management 18

35 File naming in Grid Data Resource and File Files in the Grid can be referred by different names: Logical File Name (LFN) : An alias created by a user to refer to some item of data lfn:cms/ /run2/track1 Grid Unique IDentifier (GUID) : A non-human-readable unique identifier for an item of data guid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6 Site URL (SURL) : The location of an actual piece of data on a storage system srm://storm.cnaf.infn.it:8444/infngrid/test.txt Transport URL (TURL) : Temporary locator of a replica + access protocol understood by a SE Data Management 18

36 File naming in Grid Data Resource and File Files in the Grid can be referred by different names: Logical File Name (LFN) : An alias created by a user to refer to some item of data lfn:cms/ /run2/track1 Grid Unique IDentifier (GUID) : A non-human-readable unique identifier for an item of data guid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6 Site URL (SURL) : The location of an actual piece of data on a storage system srm://storm.cnaf.infn.it:8444/infngrid/test.txt Transport URL (TURL) : Temporary locator of a replica + access protocol understood by a SE gsiftp://storm.cnaf.infn.it:2811/storage/infngrid/test.txt Data Management 18

37 File naming in Grid Files in Grid: LFN, GUID, SURL and TURL While the GUIDs and LFNs identify a file irrespective of its location, the SURLs and TURLs contain information about where a physical replica is located, and how it can be accessed. Data Management 19

38 Mapping services File Name Mapping There are two mapping: LFN > SURLs SURL > TURLs Data Management 20

39 Mapping services File Name Mapping There are two mapping: LFN > SURLs SURL > TURLs Data Management 20

40 Mapping services SURL and TURL Structure: SFN e PFN Data Management 21

41 Outline 1 Storage Element Storage services 2 GridFTP Service GridFTP Service 3 Genesis of SRM Genesis 4 File naming File naming in Grid Mapping services 5 SRM Service SRM service: main concepts Storage Area and Storage Component The Storage Resource Manager Interface Specification v2.2 6 Data access pattern Read a file Write a file 7 Conclusion Some SRM Service implementation

42 SRM service: main concepts Storage Resource Manager (SRM) Services Definition SRM services are middleware components whose function is to provide dynamic space allocation and file management in spaces for shared storage components on the Grid. SRM services implement SRM interface. Files are no longer permanent entities on the storage, but dynamic ones that can appear or disappear according to the user s specification. SRMs do not perform file transfers, but can invoke middleware components that perform this job (such as GridFTP) Data Management 23

43 SRM service: main concepts Storage Resource Manager (SRM) Services Definition SRM services are middleware components whose function is to provide dynamic space allocation and file management in spaces for shared storage components on the Grid. SRM services implement SRM interface. Files are no longer permanent entities on the storage, but dynamic ones that can appear or disappear according to the user s specification. SRMs do not perform file transfers, but can invoke middleware components that perform this job (such as GridFTP) Data Management 23

44 SRM service: main concepts Storage Resource Manager (SRM) Services Definition SRM services are middleware components whose function is to provide dynamic space allocation and file management in spaces for shared storage components on the Grid. SRM services implement SRM interface. Files are no longer permanent entities on the storage, but dynamic ones that can appear or disappear according to the user s specification. SRMs do not perform file transfers, but can invoke middleware components that perform this job (such as GridFTP) Data Management 23

45 SRM service: main concepts SRM services Data Management 24

46 SRM service: main concepts SRM role in a site In a Grid Storage Element, the SRM service provides the functionality to manage file and spaces. Data Management 25

47 SRM service: main concepts StoRM role in a site StoRM leverages on advantages of cluster file systems and standard POSIX file systems in a Grid environment. Data Management 26

48 Storage Area and Storage Component Storage Model A definition of the model for a Grid Storage Element represent the foundation to clarify the behavior of the SRM interface implementations. F. Donno et al., "Storage Element Model for SRM 2.2 and GLUE schema description, v3.5" [ link ] Data Management 27

49 Storage Area and Storage Component Space Definitions Definition Space: An SRM SPACE is a logical view of an online physical storage allocation that is reserved for read/write operations on files. A file lives within a space. Definition Static Space Reservation: It represent a Storage Area within a SE. Typically controlled by production managers of big VOs. Definition Dynamic Space Reservation: It represent a space reserved by a user through SRM functions. Data Management 28

50 Storage Area and Storage Component Storage Area and Storage Component (1/2) A Storage Element can have multiple Storage Areas Definition A Storage Area defines a portion of the total available space that can span different kinds of storage devices within a Storage Element and in case of WLCG it implements a Storage Class instance. Definition A Storage Component identifies a specific storage with certain quality properties. Data Management 29

51 Storage Area and Storage Component Storage Area and Storage Component (2/2) Data Management 30

52 Storage Area and Storage Component Recalls about Storage Quality Retention Policy, probability of data loss once stored. custodial (High Quality): Custodial quality provides low probability of loss. output (Middle Quality): Output quality is an intermediate level and refers to the data which can be replaced by lengthy or effort-full processes. replica (Low Quality): it has the highest probability of loss, but is appropriate for data that can be replaced because other copies can be accessed in a timely fashion Access Latency, On-line: Storage where files are moved to before their use Near-line: Requires latency before files can be accessed Data Management 31

53 Storage Area and Storage Component Recalls about Storage Quality in WLCG Definition storage class is a classification of quality of storage system defined in terms of the Retention Policy and Access Latency Asking for a certain storage class users can specify the desired storage system characteristics to store data. In WLCG has been decided mapping the quality of storage together with the combinations of storage devices. Custodial-Nearline, In WLCG T1D0 Custodial-Online, In WLCG T1D1 Replica-Online,In WLCG T0D1 Data Management 32

54 The Storage Resource Manager Interface Specification v2.2 SRM v2.2 functionalities The SRM functionalities can be grouped in the following categories: Data management provides capabilities to manage the data stored in a SRM, preparing envinronment for access operation (staging, etc.) and for receiving new data. Space management space can be reserved by user to have the guarantee of availability when the transfer operation takes place. Directory management, this is a set of UNIX-like directory operation used to manage the SRM namespace for creating, moving and deleting directories and files. Query functions, this set of function is used to discover information on a specific SRM endpoint. Data Management 33

55 The Storage Resource Manager Interface Specification v2.2 Synchronous and Asynchronous functionality SRM service provides provides two classes of methods: Asynchronous methods (non blocking call). Return a token corresponding to the request, the client can retrieve at any time the status of the request by addressing it through such a token. This is the case for data management functionalities. Synchronous methods (blocking call). The control is returned to the client only when the request is completed. This is the case of directory management and space management functions. Data Management 34

56 The Storage Resource Manager Interface Specification v2.2 Synchronous and Asynchronous functionality SRM service provides provides two classes of methods: Asynchronous methods (non blocking call). Return a token corresponding to the request, the client can retrieve at any time the status of the request by addressing it through such a token. This is the case for data management functionalities. Synchronous methods (blocking call). The control is returned to the client only when the request is completed. This is the case of directory management and space management functions. Data Management 34

57 The Storage Resource Manager Interface Specification v2.2 Synchronous and Asynchronous functionality SRM service provides provides two classes of methods: Asynchronous methods (non blocking call). Return a token corresponding to the request, the client can retrieve at any time the status of the request by addressing it through such a token. This is the case for data management functionalities. Synchronous methods (blocking call). The control is returned to the client only when the request is completed. This is the case of directory management and space management functions. Data Management 34

58 The Storage Resource Manager Interface Specification v2.2 srmping srmping() : used to verify the responsiveness of the service, to retrieve SRM version and other internal information. Data Management 35

59 The Storage Resource Manager Interface Specification v2.2 srmpreparetoput srmpreparetoput() : used to write files into the storage. Upon the client s request, SRM prepares a TURL so that client can write data into the TURL. Lifetime (pinning expiration time) is assigned on the TURL. target space token (Non mandatory) asynchronous operation Request token returned by SRM service Status may be checked through srmstatusofputrequest with the returned request token Data Management 36

60 The Storage Resource Manager Interface Specification v2.2 srmpreparetoget srmpreparetoget() : used to bring files online upon the client s request. It assigns TURL so that client can access the file. target space token (Non mandatory) asynchronous operation Request token returned by SRM service Status may be checked through srmstatusofgetrequest with the returned request token Data Management 37

61 The Storage Resource Manager Interface Specification v2.2 srmstatusofgetrequest and srmstatusofputrequest srmstatusofgetrequest() : used to check the status of the previously requested srmpreparetoget. Request token from srmpreparetoget must be provided. srmstatusofputrequest() : used to check the status of the previously requested srmpreparetoput. Request token from srmpreparetoput must be provided. Data Management 38

62 The Storage Resource Manager Interface Specification v2.2 srmputdone and srmreleasefiles srmputdone() : used to notify the SRM that the client completed a file transfer to the TransferURL in the allocated space. This call should normally follow srmpreparetoput. srmreleasefiles() : used to release pins on the previously requested copies (or state ) of the SURL. This function normally follows srmpreparetoget or srmbringonline functions. Data Management 39

63 The Storage Resource Manager Interface Specification v2.2 srmreservespace and srmgetspacemetadata srmreservespace() : used to reserve a space in advance for the upcoming requests to get some guarantee on the file management. Asynchronous space reservation may be necessary for some SRMs to serve many concurrent requests. srmgetspacemetadata() : used to get information of a space. Space token must be provided, and space tokens are returned upon a completion of a space reservation through srmreservespace or srmstatusofreservespacerequest. Data Management 40

64 Outline 1 Storage Element Storage services 2 GridFTP Service GridFTP Service 3 Genesis of SRM Genesis 4 File naming File naming in Grid Mapping services 5 SRM Service SRM service: main concepts Storage Area and Storage Component The Storage Resource Manager Interface Specification v2.2 6 Data access pattern Read a file Write a file 7 Conclusion Some SRM Service implementation

65 Read a file Download or Remote access (in read mode) Data Management 42

66 Write a file Upload or Remote access (in write mode) Data Management 43

67 Outline 1 Storage Element Storage services 2 GridFTP Service GridFTP Service 3 Genesis of SRM Genesis 4 File naming File naming in Grid Mapping services 5 SRM Service SRM service: main concepts Storage Area and Storage Component The Storage Resource Manager Interface Specification v2.2 6 Data access pattern Read a file Write a file 7 Conclusion Some SRM Service implementation

68 Some SRM Service implementation CASTOR-SRM [CERN and RAL] Data Management 45

69 Some SRM Service implementation Disk Pool Manager (DPM), [CERN] Data Management 46

70 Some SRM Service implementation dcache-srm, [Fermilab and DESY] Data Management 47

71 Some SRM Service implementation Storage Resource Manager (StoRM), [INFN and ICTP-EGRID] Data Management 48

72 Some SRM Service implementation Questions? Data Management 49