what if? or combining different ideas j. f. pâris

What if?orCombining different ideas

J. F. Pâris

Combining RAID-5 and LFS

RAID-5allows parallel writes thus increasing I/O

bandwidthhas problems with small writes

LFSensures that all writes are sequentialadds I/O overhead for segment cleaning

Combining RAID-5 and LFS

What would be the main advantage?

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

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 secondsDuring that time it does not need to

revalidate its cache contents sends its updates to the server

unless it has no local disk

Adding leases to NFS

What would be the main advantage of this approach?

Adding leases to NFS

What would be the main advantage of this approach? A big reduction of revalidation traffic:

Server could handle more clients

Adding leases to NFS

Would it not make the server stateful?

Adding leases to NFS

Would it not make the server stateful?Yes

Adding leases to NFS

Would it not complicate server recovery?

Adding leases to NFS

Would it not complicate server recovery?NO, because the state information would

only consist of short lived leasesA server recovering after a crash will

never have to deal with unexpired leases

Adding leases to NFS

What would you do when a lease is broken?

Adding leases to NFS

What would you do when a lease is broken?It would mean that somebody else is

accessing the fileWe could either

Return to standard NFS operation with more frequent cache refreshes

Disable client caching for a while

Adding leases to AFS/Coda

What would be the main advantage of this approach?

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

Adding leases to AFS/Coda

What would be the main disadvantage of this approach?

Adding leases to AFS/Coda

What would be the main disadvantage of this approach?Leases would have to be renewed quite

frequently