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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 - PowerPoint PPT Presentation
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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• Expose interfaces for– Space Management
(socket,SRM1.1,SRM2.1,SRM2.2)– Remote data access (gridFTP,HTTP/HTTPS)– POSIX like access (rfio)
DISK NODEDISK NODE
DPM Architecture
HEAD NODE
DISK NODES
CLIENT
METADATADPMDPNS SRM
RFIO HTTP XROOT
GRIDFTPCLI PYTHON C API NFS 4.1
DIRECT DATA
ACCESS
NFS 4.1
DPM Architecture
HEAD NODE
DPMDPNS SRM
METADATAFile and directory metadata operations
File access requests, interaction with Disk Node
daemons
Storage management via SRM clients
NFS 4.1
DISK NODEDISK NODE
DPM Architecture
DISK NODES
RFIO HTTP XROOT
GRIDFTP NFS 4.1
POSIX like access
GET / PUT operations (Apache Web Server)
File upload / download using GSI over FTP
POSIX like access
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
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
Grid Data Management
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
Grid Data Management
CLIENT INFOSYS
DCACHE
DCAP / DCAP++
GRIDFTP HTTP / WEBDAV
XROOT
CASTOR
RFIO
GRIDFTP
XROOT
DPM
RFIO
GRIDFTP HTTP
XROOT
...
…
GFAL
• Clients need knowledge of storage backend type
• Complex, hard to deploy and maintain
BDIIToA…
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
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• …
POSIX Data Access & NFS 4.1
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
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
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…
NFS 4.1 Overview
CLIENT
METADATA SERVER
DATASERVER
CONTROL PROTOCOL(undefined)
pNFS Protocol Storage Access Protocol(Layouts)
DATASERVER
…
Callbacks
NFS 4.1 Feature 1 – Unified Protocol
• One protocol, one port (2049)• Previous versions required additional
protocols– mount, lock, status, …
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
KERNEL SPACE
USER SPACE
KERNEL CLIENT
RPC.GSSDCREDENTIAL STORE
MECHGLUE
1
22
3
sec contextnegotiation
system call
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
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
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
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
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
CLIENT
NFS SITE A
NFS SITE B
1
2
open (/grid/siteB/myFile)
open (/grid/siteB/myFile)
NFS4ERR_MOVED ( fs_locations )
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
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
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)
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
NFSDMODULE
DPM NFS DAEMON
KERNEL SPACE
USER SPACE
PIPEFS
DPM API
RPC.GSSDUSER APP
NFS KERNEL CLIENT
NFS KERNEL SERVER
RPC.SVCGSSD DPM NFS DAEMON
DPM APIDPM DB
CLIENT SIDE SERVER SIDE
KERNEL SPACE
USER SPACE
DPM NFS 4.1 Picture
More Info
https://svnweb.cern.ch/trac/lcgdm/wiki/Dpm/Dev/NFS41
Data Transfer
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…
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
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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