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Sdc challenges-2012

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Sdc challenges-2012

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Sdc challenges-2012

  1. 1. GlusterFS Challenges and Futures Jeff Darcy Storage Developer Conference September 17, 2012
  2. 2. What Is GlusterFS? ● Just your basic distributed file system ● sharding, replication, striping ● Decentralized ● no central metadata server ● core functionality on clients ● Modular ● “translators”
  3. 3. Translator Stacking FUSE DHT AFR-1 Client-3Client-1 AFR-0 Client-2Client-0 ● One to one, one to many, one to zero (?) ● Rearrange, move from client to server, ...
  4. 4. Distribution (now) Server A Server BServer C File X File Y
  5. 5. Replication (now) ● Based on changelog (“dirty flags”) ● set flags, do operation, clear flags ● use flags to determine repair (“self-heal”) after failure ● Latency sensitive ● 3+ network round trips per user request ● implementation heavily optimized
  6. 6. Challenge: Multitenancy ● Focus of CloudFSHekaFS ● to be merged with GlusterFS soon-ish ● Isolate name and ID spaces ● Encrypt in flight and at rest ● Auth* ● Quota (next slide) ● Performance isolation ● cgroups
  7. 7. Challenge: Distributed Quota ● Can't trust clients to enforce quota ● Can't just divide equally among servers ● unequal usage (e.g. due to explicit placement) ● EDQUOT on one while still space on another ● “Quota rebalancing daemon” ● monitor/adjust continuously ● interesting problem at high scale
  8. 8. Challenge: Better Rebalancing ● Optimal placement vs. minimal data movement ● Different kinds of weighting Node A Node B Node C Node D Node E
  9. 9. Challenge: Replication Latency ● Reaching limits of current approach ● Have to go async? ● but still ordered ● exploit compute/data locality (e.g. Hadoop) ● journaling, conflict resolution
  10. 10. Challenge: Directory Traversal ● Piggyback attrs (and xattrs) on readdir ● Even better: cursor approach ● read everything in opendir ● zero network activity for readdir ● less current, but more consistent
  11. 11. Challenge: Many Small Files ● Prefetch whole directories ● if marked, below size threshold, ... ● Exploit async journal ● only works if compute/data colocated ● Weaken consistency? ● allow create/write/close to be buffered ● directory-level fsync (magic xattr)
  12. 12. Conclusions ● Most of these challenges are not unique to GlusterFS ● Modularity and incremental progress are preferable to monolithic “solve all problems at once” ● GlusterFS provides a good environment in which to experiment with solutions

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