Am 2018-01-20 um 19:54 schrieb Yaniv Kaul:

On Jan 19, 2018 3:29 PM, "Matthias Leopold" < <>> wrote:


    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)

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.

Thank you, but i still don't quite get what's missing.

We want to use the combination of Cinder (Ceph) + cache=writeback + VirtIO-SCSI. Would this be possible if aio=native was used (which is not configurable)? With iSCSI storage you still get cache=none when using VirtIO-SCSI and "viodiskcache=writeback" (and aio=native). Should i file a bug report for the Cinder disk situation?

Thanks again
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