[OpenAFS] Re: [ Openafs : cache on zfs ]

Dale Pontius pontius@btv.ibm.com
Thu, 03 Oct 2013 14:46:55 -0400

On 10/03/2013 02:16 PM, Andrew Deason wrote:
> On Thu, 3 Oct 2013 19:34:27 +0200
> nicolas prochazka <prochazka.nicolas@gmail.com> wrote:
>> Hello again ,
>> after some tests to use zfs as afs cache,
>> linux kernel tells :
>> BUG : soft lockup - CPU0 stuck for 23s ! [ afs_cachetrim:2908]
>> Any ideas are welcome,
> It seems pretty likely from your other message that using zfsonlinux for
> the openafs client cache is not going to work at all until someone takes
> the time to add support for it. Just use another filesystem.
> Even on other platforms, ZFS has some characteristics that make it not
> ideal for a cache, and in the past I've recommended using something else
> when it's easy to do so (e.g. UFS on Solaris, even if it's jus on a
> zvol). At least on Solaris, ZFS does some somewhat unique things with
> space allocations that have created some semi-unavoidable problems for
> the cache manager.
> I can understand if someone is using ZFS for their root fs, and they
> don't want to make a separate fs just for the cache, but if you're
> making an fs just for the cache or something, it doesn't make a lot of
> sense.
My impression has always been that journalling is not only not needed 
for the afs cache, but even not desirable.  Up until recently I'd use 
the simplest thing - an ext2 partition with noatime.  On my latest 
installs I've begun using ext4 with the journal turned off, figuring 
that with any luck afs cache blocks would map to ext4 extents, giving me 
better cache performance than even ext2.  Then again somewhere else, on 
top of no journal, I got the options:

/dev/sdb6    /var/cache/openafs    ext4 
data=writeback,barrier=0,nobh,errors=remount-ro,noatime        1 2

Dale Pontius

Dale Pontius
Senior Engineer
IBM Corporation
Phone: (802) 769-6850
Tie-Line: 446-6850
email: pontius@us.ibm.com

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