Cluster programming...

Kumaran Rajaram kums at CS.MsState.EDU
Wed Jan 22 12:21:59 EST 2003


Karl,

   What version of NFS are you using ?? File locking is supposed to
disable all client-side and server-side caching enabling file-writes to
take place immediately at the NFS server. On some NFS versions fcntl()
locks do not function correctly. Hence in order to ensure file
consistency, try installing NFSv3 and mount it with 'noac' option. NFSv3
ensures data-consistency (through stronger file-locking semantics) and
the 'noac'attribute ensures metadata consistency. Enabling 'noac' option
might hurt the I/O performance, but file consistency is guaranteed.

Cheers,
-Kums

-- Kumaran Rajaram, Mississippi State University --
kums at cs.msstate.edu  <http://www.cs.msstate.edu/~kums>




On Wed, 22 Jan 2003, Karl Bellve wrote:

>
> I am running into a little problem about multiple writes to a single
> file via NFS.
>
>
> An application is spawned on a number of nodes. When they are done, they
> all write to a specific, but non-overlapping area of the NFS mounted
> file. I use fcntl (fd, F_SETLKW, &lck) to lock to file, or wait until it
> can lock the file for writing. Fcntl() is capable to lock across NFS.
> However, some nodes fail to write their result to the file. It isn't the
> same nodes every time. I am not seeing any write errors. I tend to think
> it is a NFS caching issue. All writes get flushed before releasing the
> lock via fsync() and close().
>
> The fileserver is a Redhat 8.0 system. I uprgaded to the latest Kernel
> offered to RH8.0. That didn't fix the problem. I compiled a new kernel
> (2.4.20) and that didn't fix the problem. The nodes are Alpha's running
> RH6.2.
>
> I am thinking about alternate means of locking but fnctl() should be the
> trick.
>
>
>
>
>
>
> --
> Cheers,
>
>
>
> Karl Bellve, Ph.D.                   ICQ # 13956200
> Biomedical Imaging Group             TLCA# 7938
> University of Massachusetts
> Email: Karl.Bellve at umassmed.edu
> Phone: (508) 856-6514
> Fax:   (508) 856-1840
> PGP Public key: finger kdb at molmed.umassmed.edu
>
>
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