[OpenAFS] AFS namei file servers, SAN, any issues elsewhere? We've had some. Can AFS _cause_ SAN issues?

Kim Kimball dhk@ccre.com
Mon, 17 Mar 2008 13:33:55 -0600

Hi Jason,


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.
> Jason
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