[sheepdog-users] When does sheepdog flush the cache?

Liu Yuan namei.unix at gmail.com
Tue Jan 29 11:40:02 CET 2013

On 01/29/2013 12:07 AM, Valerio Pachera wrote:
> No way, it doesn't flush the cache when starting the guest.
> Now I'm running 0.5.5_81_g49c096c; QEMU emulator version 1.1.2
> (qemu-kvm-1.1.2+dfsg-3, Debian).

Okay, now sheepdog support restarting VM on another node without extra
manual 'collie vdi cache flush' command. The trick we do is that we
flush & delete cache automatically after VM is released(closed).

But Old QEMU has a bug to make it work and I guess QEMU 1.4 will include
this fix. (it is a small fix, I think it can be easily backported to old

So with current sheepdog and fixed QEMU, users are not expected to take
care of object cache except that QEMU daemon crashes, in which case we
need manual 'collie vdi cache flush'.

I have tested live migration with object enabled. Now object cache is
perfectly working with it, that is, after the live migration from node A
to node B, the object cache on node A will be flush & deleted and new
object cache will be activated on node B without any data integrity problem.


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