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Subject: Re: KVM HA is broken, let's fix it
From: Frank Louwers <frank@openminds.be>
In-Reply-To: <1739AED7-F5B3-4D6E-87C7-101844D10E09@schubergphilis.com>
Date: Mon, 12 Oct 2015 09:54:54 +0200
Cc: "dev@cloudstack.apache.org" <dev@cloudstack.apache.org>
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 <1739AED7-F5B3-4D6E-87C7-101844D10E09@schubergphilis.com>
To: users@cloudstack.apache.org


> On 10 Oct 2015, at 12:35, Remi Bergsma <RBergsma@schubergphilis.com> =
wrote:
>=20
> 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.=20=

>=20
> 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.=20

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=E2=80=99t need to be =
fixed.

However, HA is =E2=80=9Cnot functioning=E2=80=9D in any of these =
scenario=E2=80=99s:

- you don=E2=80=99t 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 =E2=80=9Cwizard=E2=80=9D forces you to =
configure one). You don=E2=80=99t have any active VM configured on the =
primary storage. You then perform maintenance on the NFS storage, and =
take it offline=E2=80=A6

All your hosts will then reboot, resulting in major downtime, that=E2=80=99=
s completely unnecessary. There=E2=80=99s not even an option to disable =
this at this point=E2=80=A6 We=E2=80=99ve removed the reboot =
instructions from the HA script on all our instances=E2=80=A6

Regards,

Frank=