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

[Stanislav German-Evtushenko]

On Tue, Nov 18, 2014 at 7:47 PM, Dietmar Maurer <dietmar at proxmox.com> wrote:

> > VM drives are often get corrupted when using any mode with write cache
> > enabled. Only directsync and writethrough do not produce the issue.
> Doesn't
> > matter if DRBD in master-master or master-slave mode.
> > Lars Ellenberg explains here why this happens.
>
> Sorry, but I cannot find an explaination there?
>

In short:
1) DATA from write buffer commits locally
2) DATA in write buffer changes (because write cache is enabled)
3) DATA from write buffer sends to another DRBD node
And DRBD can't catch this until integrity-alg not enabled. When enabled -
we get split brain for each occurrence for master-master or just secondary
reconnection for master-slave mode.

Best regards,
Stanislav

On Tue, Nov 18, 2014 at 7:47 PM, Dietmar Maurer <dietmar at proxmox.com> wrote:

> > VM drives are often get corrupted when using any mode with write cache
> > enabled. Only directsync and writethrough do not produce the issue.
> Doesn't
> > matter if DRBD in master-master or master-slave mode.
> > Lars Ellenberg explains here why this happens.
>
> Sorry, but I cannot find an explaination there?
>



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