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From Frank Louwers <fr...@openminds.be>
Subject Re: KVM HA is broken, let's fix it
Date Mon, 12 Oct 2015 07:54:54 GMT

> On 10 Oct 2015, at 12:35, Remi Bergsma <RBergsma@schubergphilis.com> wrote:
> 
> Can you please explain what the issue is with KVM HA? In my tests, HA starts all VMs
just fine without the hypervisor coming back. At least that is on current 4.6. Assuming a
cluster of multiple nodes of course. It will then do a neighbor check from another host in
the same cluster. 
> 
> Also, malfunctioning NFS leads to corruption and therefore we fence a box when the shared
storage is unreliable. Combining primary and secondary NFS is not a good idea for production
in my opinion. 

Well, it depends how you look at it, and what your situation is.

If you use 1 NFS export als primary storage (and only NFS), then yes, the system works as
one would expect, and doesn’t need to be fixed.

However, HA is “not functioning” in any of these scenario’s:

- you don’t use NFS as your only primary storage
- you use more than one NFS primary storage

Even worse: imagine you only use local storage as primary storage, but have 1 NFS configured
(as the UI “wizard” forces you to configure one). You don’t have any active VM configured
on the primary storage. You then perform maintenance on the NFS storage, and take it offline…

All your hosts will then reboot, resulting in major downtime, that’s completely unnecessary.
There’s not even an option to disable this at this point… We’ve removed the reboot instructions
from the HA script on all our instances…

Regards,

Frank
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