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Network File Systems

Network File Systems. Victoria Krafft CS 614 10/4/05. General Idea. People move around Machines may want to share data Want a system with: No new interface for applications No need to copy all the data No space consuming version control. Network File Systems.

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Network File Systems

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  1. Network File Systems Victoria Krafft CS 614 10/4/05

  2. General Idea • People move around • Machines may want to share data • Want a system with: • No new interface for applications • No need to copy all the data • No space consuming version control

  3. Network File Systems Diagram from http://www.cs.binghamton.edu/~kang/cs552/note11.ppt

  4. A Brief History • Network File System (NFS) developed in 1984 • Simple client-server model • Some problems • Andrew File System (AFS) developed in 1985 • Better performance • More caching client-side • SFS 1999 • NFS can be run on untrusted networks

  5. Lingering Issues • Central server is a major bottleneck • All choices still require lots of bandwidth • LANs getting faster & lower latency • Remote memory faster than local disk • ATM faster with more nodes sending data

  6. Cooperative Caching • Michael D. Dahlin, Randolph Y. Wang, Thomas E. Anderson, and David A. Patterson in 1994 • ATM, Myrinet provide faster, low-latency network • This makes remote memory 10-20x faster than disk • Want to get data from memory of other clients rather than server disk

  7. Cooperative Caching • Data can be found in: • Local memory • Server memory • Other client memory • Server disk • How should we distribute cache data?

  8. Design Decisions Private/Global Coop. Cache? Private Global Coordinated Cache Entries? Direct Client Cooperation No Coordination Coordination Greedy Forwarding Static/Dynamic Partition? Static Dynamic Block Location? N-Chance Weighted LRU Any Client Fixed Cent. Coord Hash

  9. Direct Client Cooperation • Active clients use idle client memory as a backing store • Simple • Don’t get info from other active clients

  10. Greedy Forwarding • Each client manages its local cache greedily • Server stores contents of client caches • Still potentially large amounts of data duplication • No major cost for performance improvements

  11. Centrally Coordinated Caching • Client cache split into two parts – local and global

  12. N-Chance Forwarding • Clients prefer to cache singlets, blocks stored in only one client cache. • Instead of discarding a singlet, set recirculation count to n and pass on to a random other client.

  13. Sensitivity Variation in Response Time with Client Cache Size Variation in Response Time with Network Latency

  14. Simulation results Average read response time Sever load

  15. Simulation results Slowdown Slowdown

  16. Results • N-Chance forwarding close to best possible performance • Requires clients to trust each other • Requires fast network

  17. Serverless NFS • Thomas E. Anderson, Michael D. Dahlin, Jeanna M. Neefe, David A. Patterson, Drew S. Roselli, and Randolph Y. Wang in 1995 • Eliminates central server • Takes advantage of ATM and Myrinet

  18. Starting points • RAID: Redundancy if nodes leave or fail • LFS: Recovery when system fails • Zebra: Combines LFS and RAID for distributed systems • Multiprocessor Cache Consistency: Invalidating stale cache info

  19. To Eliminate Central Servers • Scaleable distributed metadata, which can be reconfigured after a failure • Scalable division into groups for efficient storage • Scalable log cleaning

  20. How it works • Each machine has one or more roles: • Client • Storage Server • Manager • Cleaner • Management split among metadata managers • Disks clustered into stripe groups for scalability • Cooperative caching among clients

  21. xFS • xFS is a prototype of the serverless network file system • Lacks a couple features: • Recovery not completed • Doesn’t calculate or distribute new manager or stripe group maps • No distributed cleaner

  22. File Read

  23. File Write • Buffered into segments in local memory • Client commits to storage • Client notifies managers of modified blocks • Managers update index nodes & imaps • Periodically, managers log changes to stable storage

  24. Distributing File Management • First Writer – management goes to whoever created the file *does not include all local hits

  25. Cleaning • Segment utilization maintained by segment writer • Segment utilization stored in s-files • Cleaning controlled by stripe group leader • Optimistic Concurrency control resolves cleaning / writing conflicts

  26. Recovery • Several steps are O(N2), but can be run in parallel Steps For Recovery

  27. xFS Performance NFS max with 2 clients NFS max with 2 clients AFS max with 32 clients AFS max with 12 clients Aggregate Bandwidth Writing 10MB files Aggregate Bandwidth Reading 10MB files

  28. xFS Performance Average time to complete the Andrew benchmark, varying the number of simultaneous clients

  29. System Variables Aggregate Large-Write Bandwidth with Different Storage Server Configurations Variation in Average Small File Creation Speed with more Managers

  30. Possible Problems • System relies on secure network between machines, and trusted kernels on distributed nodes • Testing done on Myrinet

  31. Low-Bandwidth NFS • Want efficient remote access over slow or wide area networks • File systems better than CVS, copying all data over • Want close-to-open consistency

  32. LBFS • Large client cache containing user’s working set of files • Don’t send all the data – reconstitute files from previous data, and only send changes

  33. File indexing • Non-overlapping chunks between 2K and 64K • Broken up using 48 byte Rabin fingerprints • Identified by SHA-1 hash, indexing on first 64 bits • Stored in database, recomputed before use to avoid synchronization issues

  34. Protocol • Based on NFS, added GETHASH, MKTMPFILE, TMPWRITE, CONDWRITE, COMMITTMP • Security infrastructure from SFS • Whole file caching • Retrieve from server on read unless valid copy in cache • Write back to server when file closed

  35. File Reads

  36. File Writes

  37. Implementation • LBFS server accesses file system as an NFS client • Server creates trash directory for temporary files • Server inefficient when files overwritten or truncated, which could be fixed by lower-level access. • Client uses xfs driver

  38. Evaluation

  39. Bandwidth consumption Much higher bandwidth for first build

  40. Application Performance

  41. Bandwidth and Round Trip Time

  42. Conclusions • New technologies open up new possibilities for network file systems • Cost of increased traffic over Ethernet may cause problems for xFS, cooperative caching.

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