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Re: SAN setup - multiple machines



On Tue, 2007-07-03 at 21:33 -0400, Nilesh Bansal wrote:
> Thanks Saqib for your reply.
> 
> > > Are there any
> > > locking issues (files being modified simultaneously) than SAN can not
> > > handle.
> > yup. You need something like NFS, AFS, GFS, Lustre, or DFS to allow
> > multiple machines to access the same storage.
> 
> What happens if only one host mounts the storage for writing and all
> other hosts are read-only.
> 
> In our application, the data is stored on one machine and is updated
> often. This data is exported to other machines using NFS in a
> read-only mode. The problem with NFS is that (I think) it is slow. I
> would like to know if read performance from NFS on a gigabit lan is
> equivalent to that from a locally attached disk. Our application,
> basically a search engine, requires fast reads (iostat shows around
> 300 tps and 3000 block reads per second).


>From my understanding, the problem is write-caching and sequence of
operations on the host that has the write access. Things could be
significantly altered by the write-access host in ways that the read-
only hosts could not predict. Your read-only host will then read
corrupted data, and depending on what it's reading it could really screw
things up.

I think the only solution is to use a filesystem that is designed for
multi-host concurrent access.




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