[ovirt-users] Re: How to handle broken NFS storage?
On Fri, Jun 4, 2021 at 12:11 PM David White via Users <users(a)ovirt.org> wrote:
I'm trying to figure out how to keep a "broken" NFS mount point from
causing the entire HCI cluster to crash.
HCI is working beautifully.
Last night, I finished adding some NFS storage to the cluster - this is storage that I
don't necessarily need to be HA, and I was hoping to store some backups and
less-important VMs on, since my Gluster (sssd) storage availability is pretty limited.
But as a test, after I got everything setup, I stopped the nfs-server.
This caused the entire cluster to go down, and several VMs - that are not stored on the
NFS storage - went belly up.
Please explain in more detail "went belly up".
In general vms not using he nfs storage domain should not be affected, but
due to unfortunate design of vdsm, all storage domain share the same global lock
and when one storage domain has trouble, it can cause delays in
operations on other
domains. This may lead to timeouts and vms reported as non-responsive,
but the actual
vms, should not be affected.
If you have a good way to reproduce the issue please file a bug with
all the logs, we try
to improve this situation.
Once I started the NFS server process again, HCI did what it was
supposed to do, and was able to automatically recover.
My concern is that NFS is a single point of failure, and if VMs that don't even rely
on that storage are affected if the NFS storage goes away, then I don't want anything
to do with it.
You need to understand the actual effect on the vms before you reject NFS.
On the other hand, I'm still struggling to come up with a good
way to run on-site backups and snapshots without using up more gluster space on my (more
expensive) sssd storage.
NFS is useful for this purpose. You don't need synchronous replication, and
you want the backups outside of your cluster so in case of disaster you can
restore the backups on another system.
Snapshots are always on the same storage so it will not help.
Is there any way to setup NFS storage for a Backup Domain - as well
as a Data domain (for lesser important VMs) - such that, if the NFS server crashed, all of
my non-NFS stuff would be unaffected?
NFS storage domain will always affect other storage domains, but if you mount
your NFS storage outside of ovirt, the mount will not affect the system.
Then you can backup to this mount, for example using backup_vm.py:
https://github.com/oVirt/ovirt-engine-sdk/blob/master/sdk/examples/backup...
Or one of the backup solutions, all of them are not using a storage domain for
keeping the backups so the mount should not affect the system.
Nir