As a personal experience hosting VMs on NFS may cause your entire infrastructure to be down if you change something on TrueNAS, even adding a new NFS share may trigger a NFS server restart and suddenly all your VMs will be trashed. Emphasis on _may_.

I’ve been using the product since FreeNAS 8, which was 2012 and that’s observed behavior.

Also oVirt has its quirks with iSCSI, mainly on MPIO (Multipath I/O) but as for the combination with TrueNAS just stick with iSCSI.



The cluster is on nfs today, with 500gb NVME SiLOG. Under heavy IO the vm's are thrown into paused state instead of iowait. A prior email chain identified a code error in qemu, with a repro using nothing more than DD to set 2 gb on the virtual disk to 0's .

Since the point of the system is to handle massive IO workloads, this is obviously not acceptable.

If there is a way to make the nfs Mount more robust I'm all for it over the headaches that go with managing block io.

On Wed, Mar 2, 2022, 8:46 AM Nir Soffer <nsoffer@redhat.com> wrote:

On Wed, Mar 2, 2022 at 3:01 PM David Johnson <djohnson@maxistechnology.com> wrote:

Good morning folks, and thank you in advance.

I am working on migrating my oVirt backing store from NFS to iSCSI.

oVirt Environment:

oVirt Open Virtualization Manager
Software Version:4.4.4.7-1.el8

TrueNAS environment:

FreeBSD truenas.local 12.2-RELEASE-p11 75566f060d4(HEAD) TRUENAS amd64

The iSCSI share is on a TrueNAS server, exposed to user VDSM and group 36.

oVirt sees the targeted share, but is unable to make use of it.

The latest issue is "Error while executing action New SAN Storage Domain: Volume Group block size error, please check your Volume Group configuration, Supported block size is 512 bytes."

As near as I can tell, oVirt does not support any block size other than 512 bytes, while TrueNAS's smallest OOB block size is 4k.

This is correct, oVirt does not support 4k block storage.

 

I know that oVirt on TrueNAS is a common configuration, so I expect I am missing something really obvious here, probably a TrueNAS configuration needed to make TrueNAS work with 512 byte blocks.

Any advice would be helpful.

You can use NFS exported by TrueNAS. With NFS the underlying block size is hidden

since direct I/O on NFS does not perform direct I/O on the server.

Another way is to use Managed Block Storage (MBS) - if there a Cinder driver that can manage

your storage server, you can use MBS disks with any block size. The block size limit comes from

the traditional lvm based storage domain code. When using MBS, you use one LUN per disk, and

qemu does not have any issue working with such LUNs. 

Check with TrueNAS if they support emulating 512 block size of have another way to 

support clients that do not support 4k storage.

Nir

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