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Deferring mtime and ctime updates

Deferring mtime and ctime updates

Posted Aug 24, 2013 11:23 UTC (Sat) by jlayton (subscriber, #31672)
In reply to: Deferring mtime and ctime updates by dlang
Parent article: Deferring mtime and ctime updates

> remember that the NFS spec requires that any writes to a NFS volume must
> be safe on disk before the write completes. This requires a fsync after
> every write, which absolutely kills performance (unless you avoid ext3 and
> you have NVRAM or battery backed cache to write to), updating the
> attribute at the same time seems to be required by the standard.

That was true for NFSv2, but NFSv3 and later allow you to do UNSTABLE writes. Those don't need to be written to stable storage until the client issues a COMMIT (though the server is free to write them out earlier if it needs to). Most clients (Linux' included) will use UNSTABLE writes for the bulk of the writes that it does. STABLE (NFSv2-ish) writes are still used in some cases, but that's only where we deem that it's more efficient to do it that way.

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