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

[Eric Blevins]

I have been looking into this issue too.

cache=none and cache=directsync does not prevent the out of sync blocks on DRBD.

I have seen this on windows and linux guests.
The latest windows virtio driver from fedora should have fix to
implement flushes properly, need to test if it helps.

https://alt.fedoraproject.org/pub/alt/virtio-win/latest/images/bin/

Eric

On Thu, Dec 4, 2014 at 11:48 AM, Stanislav German-Evtushenko
<ginermail at gmail.com> wrote:
> 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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