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Lustre And Nfs V4
- 1. Lustre and NFS v4.0 Chris Sosa For Grimshaw’s Grid Seminar
- 2. Lustre – Motivation Need for a file system for large clusters that has the following attributes Highly scalable > 10,000 nodes Provide petabytes of storage High throughput (100 GB/sec) Datacenters have different needs so we need a general-purpose back-end file system
- 3. Lustre = Linux + Cluster Peter Braam created the design for Lustre at CMU whom went on to found Cluster File Systems Cluster File Systems was bought by Sun in last 2007 – Lustre now part of Sun Lustre is the file system with the largest share in HPC (see BlueGene (or not))
- 4. Features of Lustre Open-source object-based cluster file system Fully compliant with POSIX Features (i.e. what I will discuss) Object Protocols Intent-based Locking Adaptive Locking Policies Aggressive Caching
- 8. Adaptive Locking Policies Policy depends on context Mode 1: Performing operations on something they only mostly use (e.g. /home/username) Mode 2: Performing operations on a highly contentious Resource (e.g. /tmp) DLM capable of granting locks on an entire subtree and whole files
- 9. Aggressive Caching Keeps local journal of updates for locked files One per file operation Hard linked files get special treatment with subtree locks Lock revoked -> updates flushed and replayed Use subtree change times to validate cache entries Additionally features collaborative caching -> referrals to other dedicated cache service
- 10. On to NFS Version 4.0
- 11. Motivation We want a file system that provides distributed transparent access in a heterogeneous network NFS pre 4 had a lot of issues Caches had no guarantees Terrible failure semantics Hanging locks Server / Clients were never sure of anything Data coherency, what’s that?
- 12. Overview of NFS v4 Stateful Protocol Compound Operations Lease-based Locks “Delegation” to clients Close-Open Cache Consistency Better security
- 13. Stateful Borrowed model from CIFS (Common Internet File System) see MS (Marty’s supporters) Open/Close Opens also handles creates, etc. Close semantics Opens do byte locking and file locking atomically on the open Locks / delegation released on file close Everything done with file handles Always a notion of a “current file handle” i.e. see pwd
- 14. COMPOUND Ops Problem: Normal filesystem semantics have too many RPC’s (boo) Solution: Group many calls into one call (yay) Semantics Run sequentially Fails on first failure Returns status of each individual RPC in the compound response (either to failure or success) Compound Kitty
- 15. Lease-based Locks Both byte-range and file locks Heartbeats keep locks alive (renew lock) A lease on every lock that indicates that the client is still up If server fails, waits at least the agreed upon lease time (constant) before accepting any other lock requests If client fails, locks are released by server at the end of lease period
- 16. Delegation Tells client no one else has the file (similar to Lustre’s first mode) Client exposes callbacks Difference here between 4.0 / 4.1 Here’s a second bullet
- 17. Close-Open Consistency Any opens that happen after a close finishes are consistent with the information with the last close Last close wins the competition Not coherent (without locks) You have to reopen to see if you won
- 18. Security Uses the GSS-API framework All id’s are formed with [email_address] [email_address] Every implementation must have Kerberos v5 Every implementation must have LIPKey Meow
- 19. Other Stuff Replication / Migration mechanism added Special error messages to indicate migration Special attribute for both replication and migration that gives the location of the other / new location If file system response is too slow or get the special error message, can check the special attribute for the read-only replica (or stop using security)
- 20. Comparison of NFSv3 and NFSv4
- 21. Questions?