Messages in this thread | | | Date | Thu, 5 Aug 1999 18:33:57 +0200 (CEST) | Subject | Re: 2.3 SMP overlapping writes and NFS | From | Trond Myklebust <> |
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>>>>> " " == Jamie Lokier <lkd@tantalophile.demon.co.uk> writes:
> Trond Myklebust wrote: >> As long as we violate the synchronicity assumption strict >> adherence to the rule of atomicity of writes becomes a largely >> academic issue.
> They're different things.
If you cannot guarantee stability of writes, then surely atomicity cannot be guaranteed either. What if the server crashes after sending the NFS_OK, but before the data is committed?
> Regardless of committing to stable storage, write atomicity can > be used for database synchronisation between clients. Of > course any sensible client would synchronise on a single > byte... I don't know if any real applications depend on atomic > writes.
As long as the operation read+write is not atomic, can you really implement such a scheme? As Alan pointed out, link() and mkdir() are more useful for this sort of thing.
>> For NFSv3, things are of course different, since there the >> NFS_COMMIT instruction exists in order to trigger the flushing >> to disk.
> And atomicity isn't specified for NFSv3 either.
Only if you specify stable writes (FILE_SYNC) in which case the NFSv2 rules are supposed to apply.
Cheers, Trond
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