[pve-devel] NACK: [PATCH storage 2/3] krbd: remove 'exclusive-lock' from blacklist, kernel-4.13

[Alwin Antreich]

On Thu, Mar 01, 2018 at 04:23:32PM +0100, Alwin Antreich wrote:
> On Thu, Mar 01, 2018 at 10:59:15AM +0100, Fabian Grünbichler wrote:
> > this is problematic because it potentially hides bugs in our application
> > logic, with currently no benefit.
> >
> > with exclusive-locks disabled, mapping on multiple hosts is possible,
> > but mounting the same image is not (e.g., when attempting to mount, all
> > but the first successful node will fail).
> >
> > with exclusive-locks enabled, mapping and accessing/mounting is
> > sometimes possible (it seems a bit racy?), but since ext4 is not a
> > cluster FS, this will cause undesired behaviour / inconsistencies /
> > corruption.
> >
> > OTOH, with exclusive-locks enabled we would have the option of exclusive
> > mapping - if we find a way to make this work with Qemu live-migration it
> > might solve all of our problems
> >
> > TL;DR: I think we should postpone this pending further investigations
> > into potential pros and cons
> >
> I did some testing on this topic. Qemu dies when live migrating, as rbd
> can not get the lock on the new destination. A offline migration is
> possible.
>
> I guess, if we want to use it, then either we get qemu to work
> differntly on migration or only allow offline migration when
> exclusive mapping is requested.
>
> I am up for discussion.
>
>
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As to do once the kernel rbd client is able to down-/upgrade the
exclusive lock.

https://bugzilla.proxmox.com/show_bug.cgi?id=1686