[OpenAFS] AFS namei file servers, SAN, any issues elsewhere?
We've had some. Can AFS _cause_ SAN issues?
Thu, 13 Mar 2008 18:54:04 -0400
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.