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What if? or Combining different ideas

What if? or Combining different ideas. J. F. P âris. Combining RAID-5 and LFS. RAID-5 allows parallel writes thus increasing I/O bandwidth has problems with small writes LFS ensures that all writes are sequential adds I/O overhead for segment cleaning. Combining RAID-5 and LFS.

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What if? or Combining different ideas

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  1. What if?orCombining different ideas J. F. Pâris

  2. Combining RAID-5 and LFS • RAID-5 • allows parallel writes thus increasing I/O bandwidth • has problems with small writes • LFS • ensures that all writes are sequential • adds I/O overhead for segment cleaning

  3. Combining RAID-5 and LFS • What would be the main advantage?

  4. Combining RAID-5 and LFS • What would be the main advantage? • It would greatly reduce the small write penalty assuming that we can write the log one stripe at a time • Was it already tried? • Yes in the Zebra file system

  5. Adding leases to NFS • How would it work? • When a process does a lookup for a file it gets a lease on that file for up to a few seconds • During that time it does not need to • revalidate its cache contents • sends its updates to the serverunless it has no local disk

  6. Adding leases to NFS • What would be the main advantage of this approach?

  7. Adding leases to NFS • What would be the main advantage of this approach? • A big reduction of revalidation traffic: • Server could handle more clients

  8. Adding leases to NFS • Would it not make the server stateful?

  9. Adding leases to NFS • Would it not make the server stateful? • Yes

  10. Adding leases to NFS • Would it not complicate server recovery?

  11. Adding leases to NFS • Would it not complicate server recovery? • NO, because the state information would only consist of short lived leases • A server recovering after a crash will never have to deal with unexpired leases

  12. Adding leases to NFS • What would you do when a lease is broken?

  13. Adding leases to NFS • What would you do when a lease is broken? • It would mean that somebody else is accessing the file • We could either • Return to standard NFS operation with more frequent cache refreshes • Disable client caching for a while

  14. Adding leases to AFS/Coda • What would be the main advantage of this approach?

  15. Adding leases to AFS/Coda • What would be the main advantage of this approach? • No more lost callbacks • More faithful implementation of open-to-close semantics

  16. Adding leases to AFS/Coda • What would be the main disadvantage of this approach?

  17. Adding leases to AFS/Coda • What would be the main disadvantage of this approach? • Leases would have to be renewed quite frequently

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