[pve-devel] Default cache mode for VM hard drives

[Stanislav German-Evtushenko]

On Thu, Dec 4, 2014 at 7:42 PM, Dietmar Maurer <dietmar at proxmox.com> wrote:

> > > Hi Dietmar, hi Alexandre,
> > > I did manage to reproduce the issue without hardware dependency and
> > without
> > > LVM to reduce any possible influence from other components.
> >
> > IMHO this is a DRBD problem. So I think you should report that to the
> DRBD list
> > instead.
> >
> > I did and I have mentioned that.
>
> You already reported a reproducible test case?
>
>
No, but he didn't want this.
He said:
*******************************************************************
Misbehaving upper layer results in potentially divergent blocks on the DRBD
peers. Or would result in potentially divergent blocks on a local software
RAID 1.
...
Anyways.
Point being: Either have those upper layers stop modifying buffers
while they are in-flight (keyword: "stable pages").
Kernel upgrade within the VMs may do it. Changing something in the
"virtual IO path configuration" may do it. Or not.

Or live with the results, which are
potentially not identical blocks on the DRBD peers.
*******************************************************************

Stanislav
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