[sheepdog-users] Object Cache and Gateway Mode

Liu Yuan namei.unix at gmail.com
Thu Jun 21 11:09:20 CEST 2012

On 06/21/2012 04:22 PM, Bastian Scholz wrote:
> Hi,
> I have another question about object cache...
> Im using sheepdog with a gateway sheep for qemu connections.
> When enabling the object cache inside the virtual machines,
> the cache-directory of gateway sheep starts filling.
> But is it possible to limit the size of the space used for
> the object cache?

Humm, object cache reclaim is not yet implemented and very important to
put object cache to serious use. Another feature for object cache is
write through mode, which boost read performance and not compromise data
consistency at all.

Probably I'll have more time later to implement this after June release
or so. And anyone is welcome to implement this features, I think they
are good starting point to take part in development of Sheepdog.

> I have only a small partition for the gateway sheep, if it
> is filled with cached object, the gateway stops working and
> gives a "No space left on device" message.
> I could resize this partition for the moment, but as far as
> I understand at the moment, the corner case means, that the
> object cache must hold all objects of the cluster. So the
> cache partition must be as big as the rest of the cluster...

Object cache is per VDI cache, so you can choose which VDI to cache by
QEMU start command as a workaround (assume partition can hold all
objects of this VDI). Yes for a long run, object cache reclaim will make
object cache more appealing and useful.


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