[sheepdog] [PATCH 1/4] dog: make consistency check optional

[MORITA Kazutaka]

At Thu, 22 Aug 2013 14:02:59 +0800,
Liu Yuan wrote:
> 
> On Thu, Aug 22, 2013 at 01:01:40PM +0900, MORITA Kazutaka wrote:
> > From: MORITA Kazutaka <morita.kazutaka at lab.ntt.co.jp>
> > 
> > This splits vdi check into replica existence check and replica
> > consistency check, and make consistency check optional.  It is because:
> > 
> >  - Existence check can be done even when there is a VM who uses the
> >    vdi.
> > 
> >  - Existence check doesn't need to calculate sha1 values and it is
> >    much faster than consistency check.
> > 
> >  - Existence check is more important because write requests are
> >    rejected when one of the replicas is missing.
> > 
> >  - In most cases, replica inconsistency doesn't cause a problem
> >    because the client should have received EIO when the consistency
> >    problem happened and the client shouldn't use the inconsistent area
> >    without updating the area again.
> 
> Make existence check default looks okay to me, but then can we fix not_found
> object by 'vdi check' without -C?

I think yes.  Fixing no object can be run even when the vm is still
using the vdi, I guess.  This is another reason why we should split
'-C' and '-A'.

Thanks,

Kazutaka