[OpenAFS] AFS namei file servers, SAN, any issues elsewhere?
We've had some. Can AFS _cause_ SAN issues?
Mon, 17 Mar 2008 13:33:25 -0600
Robert Banz wrote:
> AFS can't really cause "san issues" in that it's just another
> application using your filesystem. In some cases, it can be quite a
> heavy user of such, but since its only interacting through the fs, its
> not going to know anything about your underlying storage fabric, or
> have any way of targeting it for any more badness than any other
> filesystem user.
That's what I thought. Todd's message about the changes to code to
reduce inode creation times aside.
> One of the big differences that would effect the filesystem IO load
> that occurred between 1.4.1 & 1.4.6 was the removal functions that
> made copious fsync operations. These operations were called in
> fileserver/volserver functions that modified various in-volume
> structures, specifically file creations and deletions, and would lead
> to rather underwhelming performance when doing vos restores, deleting,
> or copying large file trees. In many configurations, this causes the
> OS to pass on a call to the underlying storage to verify that all
> changes written have been written to *disk*, causing the storage
> controller to flush its write cache. Since this defeats many of the
> benefits (wrt I/O scheduling) on your storage hardware of having a
> cache, this could lead to overloaded storage.
Right. We saw significant improvement on the Hitachi 9585 when we
upgraded to 1.4.6. The Hitachi USP continues to spew scsi command timeouts.
> Some storage devices have the option to ignore these calls from
> devices, assuming your write cache is reliable.
> Under UFS, I would suggest that you'd be running in 'logging' mode
> when using the namei fileserver on Solaris, as yes, fsck is rather
> horrible to run. Performance on reasonably recent versions of ZFS
> were quite acceptable as well.
Yep, we're running in logging mode. Unfortunately Solaris doesn't allow
me to relocate the log -- it has to be on the same partition that is
experiencing the command timeouts -- and when the UFS log write timeout
occurs Solaris unmounts the partition and asks for (drum roll) you
guessed it! fsk
> Anyhow, hope this is of some help.
Tons. Thanks Rob.
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