[Sheepdog] [PATCH] sheep: disable object cache by default

[MORITA Kazutaka]

At Tue, 08 May 2012 10:25:56 +0800,
Liu Yuan wrote:
> 
> On 05/08/2012 01:48 AM, MORITA Kazutaka wrote:
> 
> > At Mon, 07 May 2012 10:53:31 +0800,
> > Liu Yuan wrote:
> >>
> >> On 05/07/2012 03:37 AM, MORITA Kazutaka wrote:
> >>
> >>> Though it is important to support a write caching feature in Sheepdog,
> >>> I think we should disable it by default for now because there are
> >>> still some cache coherency problems which looks hard to solve:
> >>
> >>
> >> Disagree with the patch.
> >>
> >> QEMU setup already disables object cache as default (writethrough mode).
> >> If users explicitly enables, he knows better than us to do such a policy.
> > 
> > qemu-img uses cache=unsafe or cache=writeback by default, so the users
> > may implicitly enable it.
> > 
> 
> 
> So a document would solve it.

I know that the object cache works well if we don't mix writeback and
writethrough requests.  But the default cache modes of qemu and
qemu-img are different, so, IMHO, the object cache really should
handle the case.

If you really don't want to disable the feature by default, how about
just adding an option to disable the object cache?  If we can disable
it with a sheep command line option, it's okay, at least to me.

Thanks,

Kazutaka