[ovirt-devel] [vdsm] VM recovery now depends on HSM

[Michal Skrivanek]

On Jul 8, 2014, at 22:36 , Adam Litke <alitke at redhat.com> wrote:

> Hi all,
> 
> As part of the new live merge feature, when vdsm starts and has to
> recover existing VMs, it calls VM._syncVolumeChain to ensure that
> vdsm's view of the volume chain matches libvirt's.  This involves two
> kinds of operations: 1) sync VM object, 2) sync underlying storage
> metadata via HSM.
> 
> This means that HSM must be up (and the storage domain(s) that the VM
> is using must be accessible.  When testing some rather eccentric error
> flows, I am finding this to not always be the case.
> 
> Is there a way to have VM recovery wait on HSM to come up?  How should
> we respond if a required storage domain cannot be accessed?  Is there
> a mechanism in vdsm to schedule an operation to be retried at a later
> time?  Perhaps I could just schedule the sync and it could be retried
> until the required resources are available.

I've briefly discussed with Federico some time ago that IMHO the syncVolumeChain needs to be changed. It must not be part of VM's create flow as I expect this quite a bottleneck in big-scale environment (it is now in fact not executing only on recovery but on all 4 create flows!).
I don't know how yet, but we need to find a different way. Now you just added yet another reason.

So…I too ask for more insights:-)

Thanks,
michal

> 
> Thanks for your insights.
> 
> -- 
> Adam Litke
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