[ovirt-users] Re: How to handle broken NFS storage?

Discussion:

Vojtech Juranek

2021-06-04 12:01:23 UTC

what was the error? Was NFS domain master storage domain?

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. 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.
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?
Sent with ProtonMail Secure Email.

Nir Soffer

2021-06-04 16:29:24 UTC

Permalink

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.

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_vm.py

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
_______________________________________________
Users mailing list -- ***@ovirt.org
To unsubscribe send an email to users-***@ovirt.org
Privacy Statement: https://www.ovirt.org/privacy-policy.html
oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/
List Archives: https://lists.ovirt.org/archives/list/***@ovirt.org/message/MYQA

Nir Soffer

2021-06-06 09:31:22 UTC

Permalink

When I stopped the NFS service, I was connect to a VM over ssh.
I was also connected to one of the physical hosts over ssh, and was running top.
I observed that server load continued to increase over time on the physical host.
Several of the VMs (perhaps all?), including the one I was connected to, went down due to an underlying storage issue.
Jun 4, 2021, 4:25:42 AM
Highly Available VM server2.example.com failed. It will be restarted automatically.

Do you have a cdrom on an ISO storage domain, maybe on the same NFS server
that you stopped?

Jun 4, 2021, 4:25:42 AM
Highly Available VM mail.example.com failed. It will be restarted automatically.
Jun 4, 2021, 4:25:42 AM
Highly Available VM core1.mgt.example.com failed. It will be restarted automatically.
Jun 4, 2021, 4:25:42 AM
VM cha1-shared.example.com has been paused due to unknown storage error.
Jun 4, 2021, 4:25:42 AM
VM server.example.org has been paused due to storage I/O problem.
Jun 4, 2021, 4:25:42 AM
VM server.example.com has been paused.

I guess this vm was using the NFS server?

Jun 4, 2021, 4:25:42 AM
VM server.example.org has been paused.
Jun 4, 2021, 4:25:41 AM
VM server.example.org has been paused due to unknown storage error.
Jun 4, 2021, 4:25:41 AM
VM HostedEngine has been paused due to storage I/O problem.
During this outage, I also noticed that customer websites were not working.
So I clearly took an outage.

If you have a good way to reproduce the issue please file a bug with
all the logs, we try to improve this situation.

I don't have a separate lab environment, but if I'm able to reproduce the issue off hours, I may try to do so.
What logs would be helpful?

/var/log/vdsm.log
/var/log/sanlock.log
/var/log/messages or output of journalctl

If I'm understanding you correctly, it sounds like you're suggesting that I just connect 1 (or multiple) hosts to the NFS mount manually,

Yes

and don't use the oVirt manager to build the backup domain. Then just run this script on a cron or something - is that correct?

Yes.

You can run the backup in many ways, for example you can run it via ssh
from another host, finding where vms are running, and connecting to
the host to perform a backup. This is outside of ovirt, since ovirt does not
have built-in a backup feature. We have backup API and example code using it
which can be used to build a backup solution.

Sent with ProtonMail Secure Email.
‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐

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.

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.
https://github.com/oVirt/ovirt-engine-sdk/blob/master/sdk/examples/backup_vm.py
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
Privacy Statement: https://www.ovirt.org/privacy-policy.html
oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/

_______________________________________________
Privacy Statement: https://www.ovirt.org/privacy-policy.html
oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/

_______________________________________________
Users mailing list -- ***@ovirt.org
To unsubscribe send an email to users-***@ovirt.org
Privacy Statement: https://www.ovirt.org/privacy-policy.html
oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/
List Archives: https://lists.ovirt.org/archives/list/***@ovirt.org/message/SP

Nir Soffer

2021-06-06 09:35:10 UTC

Permalink

Post by Nir Soffer

Do you have a cdrom on an ISO storage domain, maybe on the same NFS server
that you stopped?

If you share vm xml for the ha vms and the regular vms it will be easier to
understand your system.

The best way is to use:

sudo virsh -r dumpxml {vm-name}

Post by Nir Soffer

I guess this vm was using the NFS server?

If you have a good way to reproduce the issue please file a bug with
all the logs, we try to improve this situation.

I don't have a separate lab environment, but if I'm able to reproduce the issue off hours, I may try to do so.
What logs would be helpful?

/var/log/vdsm.log
/var/log/sanlock.log
/var/log/messages or output of journalctl

If I'm understanding you correctly, it sounds like you're suggesting that I just connect 1 (or multiple) hosts to the NFS mount manually,

Yes

and don't use the oVirt manager to build the backup domain. Then just run this script on a cron or something - is that correct?

Yes.
You can run the backup in many ways, for example you can run it via ssh
from another host, finding where vms are running, and connecting to
the host to perform a backup. This is outside of ovirt, since ovirt does not
have built-in a backup feature. We have backup API and example code using it
which can be used to build a backup solution.

Sent with ProtonMail Secure Email.
‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐

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.

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?

_______________________________________________
Privacy Statement: https://www.ovirt.org/privacy-policy.html
oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/

Edward Berger

2021-06-05 14:32:36 UTC

Permalink

I could be mistaken, but I think the issue is that ovirt engine believes
the NFS domain is mandatory for all hypervisor hosts unless you put the
storage domain into 'maintenance' mode.
It will notice its down and start trying to fence the offending hypervisors
which in turn tries to migrate VMs to other hypervisors that also are
marked bad because they can't reach the storage domain either. That's what
I recall once seeing when I thought it was safe to temporarily take down an
ISO NFS domain a few years ago.

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.
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.
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.
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?
Sent with ProtonMail <https://protonmail.com> Secure Email.
_______________________________________________
Privacy Statement: https://www.ovirt.org/privacy-policy.html
https://www.ovirt.org/community/about/community-guidelines/