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

[Stanislav German-Evtushenko]

On Thu, Nov 20, 2014 at 10:22 AM, Dietmar Maurer <dietmar at proxmox.com>
wrote:

> > Yes, so DRBD gets the data, and kvm send sync request when required. So
> I still
> > not
> > see the problem.
> > Can you also reproduce the problems if you use DRBD device directly,
> without
> > LVM on top?
> >
> > Yes, it is reproducible without LVM.
>
> OK. So is there some 'official' Documentation from DRBD people, stating
> that we
> need to use 'cache=writethrough' with qemu?
>

No. All I could get is in this thread:
http://www.gossamer-threads.com/lists/drbd/users/25946
Lars is a main DRBD developer.

BTW, not only cache=writethrough but also cache=directsync. Writethrough is
host RAM hungry and also requires extra time to 'copy memory'. So for some
cases directsync can be more suitable.
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