[OpenAFS] AFS namei file servers, SAN, any issues elsewhere?
We've had some. Can AFS _cause_ SAN issues?
Mon, 17 Mar 2008 13:33:55 -0600
Can you tell me which flavor of SAN you're using?
Jason Edgecombe wrote:
> 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.
>> 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.
>> 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.
> I can confirm Robert's observations. I recently tested openafs 1.4.1
> inode vs 1.4.6 namei on solaris 9 sparc with a Sun Storedge 3511
> Expansion tray fibre channel device. The difference is stagerring with
> vos move and such. We have been using the 1.4.6 namei config on a SAN
> for a few months now with no issues.
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