Currently, viodiskcache property does not work on 4.2 - setting Regression keyword.

This bug report has Keywords: Regression or TestBlocker.
Since no regressions or test blockers are allowed between releases, it is also being identified as a blocker for this release. Please resolve ASAP.

verified on build rhv-release-4.2.2-4-001.noarch

1. Create disk (Storage /Disks/Images) with profile nfs_0, Interface VirtIO.
2. Create VM with this disk.
3. Create Custom Property "viodiskcach = none"
3. On host run <virsh -r dumpxml 21>
    result:
    <ovirt-vm:custom>
        <ovirt-vm:viodiskcache>none</ovirt-vm:viodiskcache>
    </ovirt-vm:custom>
4. change the value of Custom Property "viodiskcach = writeback"
    result:
    <ovirt-vm:custom>
        <ovirt-vm:viodiskcache>writeback</ovirt-vm:viodiskcache>
    </ovirt-vm:custom>
5. change the value of Custom Property "viodiskcach = writethrough"
    result:
     <ovirt-vm:custom>
        <ovirt-vm:viodiskcache>writethrough</ovirt-vm:viodiskcache>
    </ovirt-vm:custom>

The same steps are performed with VirtIO-SCSI Interface disk.

(In reply to Polina from comment #3)
> verified on build rhv-release-4.2.2-4-001.noarch
> 
> 1. Create disk (Storage /Disks/Images) with profile nfs_0, Interface VirtIO.
> 2. Create VM with this disk.
> 3. Create Custom Property "viodiskcach = none"
> 3. On host run <virsh -r dumpxml 21>
>     result:
>     <ovirt-vm:custom>
>         <ovirt-vm:viodiskcache>none</ovirt-vm:viodiskcache>
>     </ovirt-vm:custom>
> 4. change the value of Custom Property "viodiskcach = writeback"
>     result:
>     <ovirt-vm:custom>
>         <ovirt-vm:viodiskcache>writeback</ovirt-vm:viodiskcache>
>     </ovirt-vm:custom>
> 5. change the value of Custom Property "viodiskcach = writethrough"
>     result:
>      <ovirt-vm:custom>
>         <ovirt-vm:viodiskcache>writethrough</ovirt-vm:viodiskcache>
>     </ovirt-vm:custom>
> 
> The same steps are performed with VirtIO-SCSI Interface disk.

Polina, please verify that the cache is set in the 'driver' element of the 'disk'. It should be something like:
<disk ... >
 ...
 <driver cache="writethrough" ... />
 ...
</disk>

yes, it appears under disk element:

    <disk type='file' device='cdrom'>
      <driver error_policy='report'/>
      <source startupPolicy='optional'/>
      <target dev='hdc' bus='ide'/>
      <readonly/>
      <alias name='ua-fc8fd256-bcf9-4994-bced-353c56e67334'/>
      <address type='drive' controller='0' bus='1' target='0' unit='0'/>
    </disk>
    <disk type='file' device='disk' snapshot='no'>
      <driver name='qemu' type='raw' cache='writeback' error_policy='stop' io='threads'/>
      <source file='/rhev/data-center/mnt/yellow-vdsb.qa.lab.tlv.redhat.com:_Compute__NFS_GE_compute-ge-3_nfs__0/8ac34f0b-b74a-48b7-bb81-9f5d112cf196/images/43ef6129-cc20-459a-bcce-fa5d9cff2962/a2510013-7c45-4b04-9c0a-93c83a3e9790'/>
      <backingStore/>
      <target dev='vda' bus='virtio'/>
      <serial>43ef6129-cc20-459a-bcce-fa5d9cff2962</serial>
      <alias name='ua-43ef6129-cc20-459a-bcce-fa5d9cff2962'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
    </disk>

(In reply to Polina from comment #5)
Thanks, so that is verified then.

This bugzilla is included in oVirt 4.2.2 release, published on March 28th 2018.

Since the problem described in this bug report should be
resolved in oVirt 4.2.2 release, it has been closed with a resolution of CURRENT RELEASE.

If the solution does not work for you, please open a new bug report.