[Sheepdog] [PATCH v5 4/8] sheep: teach sheep to use object cache

Liu Yuan namei.unix at gmail.com
Mon Mar 26 06:15:29 CEST 2012

On 03/26/2012 04:41 AM, MORITA Kazutaka wrote:

> Consider that the object is dirty if the VDI was opened with a
> writeback mode in the previous time.  I think we need to check a cache
> here.

For the sane usage, VMs should not be opened both for none-cache and
cache mode off and on. Even if VM first open the vdi with cache mode
first, then want to use none-cache mode, current implementation would be
okay, since after the guest was closed, the dirty bits would be flushed
to the cluster.

So the problem is precisely that we can't handle the situation that VM
runs with cache first, then crashes, then boots up again without cache.
We'd better use qemu-io to issue a flush requests first manually, then
we can safe boot the VM without cache, not losing any dirty data.

So I don't think it worth introducing complexity to object cache to
handle this corner case that already should be handled by other means.


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