Does it help if you edit the VM and under Resource Allocation – enable IO threads. ?

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From: <users-bounces@ovirt.org> on behalf of Yaniv Kaul <ykaul@redhat.com>
Date: Saturday, January 20, 2018 at 12:54 PM
To: Matthias Leopold <matthias.leopold@meduniwien.ac.at>
Cc: Wolfgang Lendl <wolfgang.lendl@meduniwien.ac.at>, Ovirt Users <users@ovirt.org>
Subject: Re: [ovirt-users] VirtIO-SCSI and viodiskcache custom property

On Jan 19, 2018 3:29 PM, "Matthias Leopold" <matthias.leopold@meduniwien.ac.at> wrote:

Hi,

is there a reason why the viodiskcache custom property isn't honored when using VirtIO-SCSI?

On a Cinder (Ceph) disk "viodiskcache=writeback" is ignored with VirtIO-SCSI and honored when using VirtIO.

On an iSCSI disk "viodiskcache=writeback" is ignored with VirtIO-SCSI and the VM can't be started when using VirtIO with "unsupported configuration: native I/O needs either no disk cache or directsync cache mode, QEMU will fallback to aio=threads"

We actually want to use "viodiskcache=writeback" with Cinder (Ceph) disks.

That's because on block storage we use native io and not threads. I assume the hook needs to change to use native io in this case. 

Y. 

oVirt version: 4.1.8

Thanks
Matthias

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