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Standards in DPM

Standards in DPM. Outline. Disk Pool Manager (DPM) Grid Data Management Why Standards POSIX Access (NFS4.1) HTTP / WebDAV. Disk Pool Manager (DPM). DPM Main Goals. Provide lightweight “grid enabled” storage Manage space on distributed disk servers Manage a hierarchical namespace

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Standards in DPM

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  1. Standards in DPM

  2. Outline • Disk Pool Manager (DPM) • Grid Data Management • Why Standards • POSIX Access (NFS4.1) • HTTP / WebDAV

  3. Disk Pool Manager (DPM)

  4. DPM Main Goals • Provide lightweight “grid enabled” storage • Manage space on distributed disk servers • Manage a hierarchical namespace • Expose interfaces for • Space Management (socket,SRM1.1,SRM2.1,SRM2.2) • Remote data access (gridFTP,HTTP/HTTPS) • POSIX like access (rfio)

  5. DPM Architecture HEAD NODE METADATA DPNS DPM SRM NFS 4.1 CLIENT GRIDFTP NFS 4.1 CLI PYTHON C API XROOT RFIO HTTP DIRECT DATA ACCESS DISK NODES DISK NODE DISK NODE

  6. DPM Architecture File and directory metadata operations HEAD NODE METADATA DPNS DPM SRM NFS 4.1 File access requests, interaction with Disk Node daemons Storage management via SRM clients

  7. DPM Architecture POSIX like access File upload / download using GSI over FTP GET / PUT operations (Apache Web Server) GRIDFTP NFS 4.1 XROOT RFIO HTTP DISK NODES DISK NODE POSIX like access DISK NODE

  8. DPM Main Features • Separation of data and metadata • Hierarchical namespace • /dpm/<domain>/home/<vo> • Strong security • X509 & KRB5 (auth), VOMS & Virtual IDs (authz) • UNIX like commands • dpns-ls, dpns-mkdir, dpns-<usual-command-here> • Database centric • Support for MySQL, Oracle and PostgreSQL, easily load balanced • SLC4/5 and Solaris for server side, Debian clients, prototype for MacOSX clients

  9. DPM Further Details • Written mostly in C • Statistics from GStat • https://gstat-wlcg.cern.ch/gstat/stats/ • Over 200 grid sites use DPM • Largest deployment: 1.2PB • More Information • https://svnweb.cern.ch/trac/lcgdm/wiki/Dpm

  10. Grid Data Management

  11. Grid Data Management • Heterogeneous environment • > 250 sites in total • DPM is one of multiple storage elements • Others are CASTOR, dCache, STORM/GPFS, … • SRM is the only “standard” protocol • Helps, but only for space management • And even here implementations differ • No standard protocol for data access • rfio, dcap(++), xroot

  12. Grid Data Management BDII INFOSYS GFAL CLIENT ToA … CASTOR DCACHE DPM ... … RFIO XROOT DCAP / DCAP++ XROOT RFIO XROOT GRIDFTP GRIDFTP HTTP / WEBDAV GRIDFTP HTTP • Clients need knowledge of storage backend type • Complex, hard to deploy and maintain

  13. Grid Data Management • Library dependency issues • Requirement of user interfaces (UIs) • Entry points to the grid • Maintained by experts • Very hard to use “standard” distributions • Even transition from SLC4 to 5 is problematic • Validation takes a long time

  14. Why Standards? • Accessibility • Not limiting access to OS X version Y with library Z • Validation • Using common validation and test tools • Stability • Evolution discussed in a wide group • Ease of implementation • Sharing of experiences, common code base • No vendor lock-in • …

  15. POSIX Data Access & NFS 4.1

  16. POSIX Data Access • We have some specific requirements • Strong authentication • Ideally using X509 certificates • Support for clustered filesystems • Separation of data and metadata access • (Global?) Hierarchical namespace • Performance (even in WAN) NFS4.1 offers all of this… and more • We now have a standard we can use • It’s just POSIX, no need for any additional library

  17. Some NFS History • NFS2 in 1989 (RFC 1094) • NFS1 was Sun internal • NFS3 in 1995 (RFC 1813) • Large file support (64bit) • Performance enhancements (transfer buffer, num round trips) • NFS4 in 2003 (RFC 3010) • Better WAN performance • Strong security • Locking • Delegations • Callbacks • Backwards compatible extensions • NFS4.1 in 2010 (RFC 5661) • Main feature is parallel NFS

  18. NFS 4.1 • IETF Standard (RFC 5661) • Different in nature from previous versions • Parallelism is the key word • No single server bottleneck • Meets needs of HPC and clustered systems • Supported by major vendors • Let’s look a bit in detail…

  19. NFS 4.1 Overview CLIENT Callbacks pNFS Protocol Storage Access Protocol (Layouts) DATA SERVER METADATA SERVER DATA SERVER CONTROL PROTOCOL (undefined) …

  20. NFS 4.1 Feature 1 – Unified Protocol • One protocol, one port (2049) • Previous versions required additional protocols • mount, lock, status, …

  21. NFS 4.1 Feature 2 – Strong Auth(z) • Based on RPCSEC_GSS (RFC 2203) • Support for multiple security mechanisms • KRB5 is mandatory, negotiation is in the protocol • Working to have X509 support (probably via globus GSSAPI plugin) • String based identities • Basic permissions + ACLs • Example: Linux Client 1 3 KERNEL CLIENT system call KERNEL SPACE MECHGLUE 2 USER SPACE RPC.GSSD 2 sec context negotiation CREDENTIAL STORE

  22. NFS 4.1 Feature 3 – Bulk Operations • Protocol defines only two procedures • NULL and COMPOUND • COMPOUND procedure holds Operations • Open, Read, Write, Close, … • Much less round trips • Better performance, especially over WAN

  23. NFS 4.1 Feature 4 - Sessions • Decouples transport (connection) from client • Persistent state on the server • Locks, opens, delegations, layouts, … • Multiple connections per session (from the same client) • Multiple sessions per client • Exactly Once Semantics (EOS) • Even in failure/recovery, thanks to reply cache

  24. NFS 4.1 Feature 5 - Delegations • Given for files and directories • Moves part of the logic from server to client • Regarding access permissions, … • Multiple types of delegations • Can be recalled (via callback) • On conflicting request from other client • Improved Performance • Less round trips

  25. NFS 4.1 Feature 6 - Layouts • Describe how to access data in storage • Multiple storage protocols supported • File, Object (RFC 5663), Block (RFC 5664) • Striping available with pNFS File Layout • Clients must request layout to MD server • Storage servers refuse access if request does not match layout • Layouts can be recalled, via callback • Ex: change in access permissions

  26. NFS 4.1 Feature 7 – Multi Server Namespace • Namespace spawning multiple domains • Servers redirect clients when data is not local • Redirection is the key word here • Can also be used to provide clients with alternative locations NFS SITE A open (/grid/siteB/myFile) 1 NFS4ERR_MOVED ( fs_locations ) CLIENT 2 NFS SITE B open (/grid/siteB/myFile)

  27. NFS 4.1 Additional Goodies • Clients provided by industry • Linux, Solaris, Windows • Free client caching • It’s just there… we benefit from experts implementing caching in the OS • Support from major industry vendors • Netapp, Panasas, IBM, Oracle, EMC • Waiting for wide client availability • dCache also has support for NFS4.1

  28. NFS 4.1 Client Availability • Linux since 2.6.32 • pNFS part coming with 2.6.36 • pNFS builds in Fedora 12, 13 • We also keep a debian one  • pNFS expected in RHEL 6.1 • Solaris driver available (but not shipped yet) • Windows driver available

  29. DPM NFS4.1 Implementation • Aiming for a basic prototype by end of August • Additional frontend in the DPM Head Node • Possible to reuse existing implementations • Benefit from implementing a standard • Kernel Space: Linux spnfs • User Space: Ganesha (CEA)

  30. DPM NFS4.1 Implementation • Based on sPNFS • A prototype pNFS server implementation for Linux • Done as a proof of concept, but good for us to use as a starting point • Still, a lot of the code can be reused • We integrate the name server requests with the DPM API NFSD MODULE KERNEL SPACE PIPEFS USER SPACE DPM NFS DAEMON DPM API

  31. DPM NFS 4.1 Picture CLIENT SIDE SERVER SIDE NFS KERNEL SERVER NFS KERNEL CLIENT KERNEL SPACE USER SPACE DPM NFS DAEMON USER APP RPC.GSSD RPC.SVCGSSD DPM DB DPM API

  32. More Info https://svnweb.cern.ch/trac/lcgdm/wiki/Dpm/Dev/NFS41

  33. Data Transfer

  34. HTTP (s) • DPM already supports HTTP (s) • As a transfer protocol • Easy authentication / authorization • Newer versions of openssl with X509 proxy support make this even easier • Implemented as an apache module or cgi • Firewall friendly • Clients? They are everywhere…

  35. WebDAV • Extensions to HTTP 1.1 for document management (RFC 2518) • Enables wide collaboration • Locking • Namespace management (copy, move, …) • Metadata / properties on files • Maybe not so interesting for HEP users • But very popular within other communities • dCache has had very good feedback on it • Implementation not yet scheduled, but in the plan

  36. Conclusions • Our environment is not standards friendly • Standard protocols exist today fitting all our use cases • Benefits for users, developers, admins • Usability, maintainability, evolution • DPM will continue focusing on standards • And will soon use them for all our use cases • Ongoing work also within the EMI data management group in the same direction

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