[OpenAFS] /var/cache/openafs on btrfs

[Benjamin Kaduk]

On Wed, 2 Mar 2016, Fred Drueck wrote:

> Hello Everyone,
>
> According to the OpenAFS admin FAQ, it appears that the officially
> supported file systems for the disk cache are:
>
> ext2
> ext3
> hfs (HP-UX)
> xfs (at least on IRIX 6.5)
> ufs (Solaris, ?Tru64Unix)
>
> which is clearly out of date, since there is a working implementation for
> OS X that runs on top of HFS+
>
> For some time I've been fearlessly using both ext4 and btrfs (on Linux, as
> you might infer) as the backing storage for my AFS client cache.
>
> I have noticed some fairly rare issues with the clients if all file/db
> servers (in our cell the same machines) become unavailable.  The '/afs'
> mount becomes un-accessible and attempts to access files often result in
> very long timeouts.  I've always been able to fix things by somehow

long timeouts are expected when all the db servers are inaccessible.

> shutting down the client (in the worst case by physical power-off and
> reboot into single user mode) and deleting the cache.
>
> Is there some chance that this is because I've been causing these problems
> by using un-supported file-systems as the backing storage for the client
> cache?

I think there is some chance, but this is not an area I've looked into for
quite some time, and may be misremembering.

I do have some recollection that ZFS behaves poorly for a cache partition,
and given btrfs's similarities to ZFS, would not really recommend it
either, absent further research.

-Ben