Hi Nir,

El 25/06/16 a las 22:57, Nir Soffer escribió:

On Sat, Jun 25, 2016 at 11:47 PM, Nicolás <nicolas@devels.es> wrote:

Hi,

We're using Ceph along with an iSCSI gateway, so our storage domain is
actually an iSCSI backend. So far, we have had zero issues with cca. 50 high
IO rated VMs. Perhaps [1] might shed some light on how to set it up.

Can you share more details on this setup and how you integrate with ovirt?

For example, are you using ceph luns in regular iscsi storage domain, or
attaching luns directly to vms?

Fernando Frediani (responding to this thread) hit the nail on the head. Actually we have a 3-node Ceph infrastructure, so we created a few volumes on the Ceph nodes side (RBD) and then exported them to iSCSI, so it's oVirt who creates the LVs on the top, this way we don't need to attach luns directly.

Once the volumes are exported on the iSCSI side, adding an iSCSI domain on oVirt is enough to make the whole thing work.

As for experience, we have done a few tests and so far we've had zero issues:

• The main bottleneck is the iSCSI gateway interface bandwith. In our case we have a balance-alb bond over two 1G network interfaces. Later we realized this kind of bonding is useless because MAC addresses won't change, so in practice only 1G will be used at most. Making some heavy tests (i.e., powering on 50 VMs at a time) we've reached this threshold at specific points but it didn't affect performance significantly.

• Doing some additional heavy tests (powering on and off all VMs at a time), we've reached the maximum value of cca. 1200 IOPS at a time. In normal conditions we don't surpass 200 IOPS, even when these 50 VMs do lots of disk operations.
• We've also done some tolerance tests, like removing one or more disks from a Ceph node, reinserting them, suddenly shut down one node, restoring it... The only problem we've experienced is a slower access to the iSCSI backend, which results in a message in the oVirt manager warning about this: something like "Storage is taking to long to respond...", which was maybe 15-20 seconds. We got no VM pauses at any time, though, nor any significant issue.

Did you try our dedicated cinder/ceph support and compared it with ceph
iscsi gateway?

Not actually, in order to avoid deploying Cinder we directly implemented the gateway as it looked easier to us.

Nir

Hope this helps.

Regards.

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