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From Syed Ahmed <sah...@cloudops.com>
Subject Re: Adding VirtIO SCSI to KVM hypervisors
Date Sat, 21 Jan 2017 15:15:33 GMT
Wido,

Were you thinking of adding this as a global setting? I can see why it will
be useful. I'm happy to review any ideas you might have around this.

Thanks,
-Syed
On Sat, Jan 21, 2017 at 04:46 Laszlo Hornyak <laszlo.hornyak@gmail.com>
wrote:

> Hi Wido,
>
> If I understand correctly from the documentation and your examples, virtio
> provides virtio interface to the guest while virtio-scsi provides scsi
> interface, therefore an IaaS service should not replace it without user
> request / approval. It would be probably better to let the user set what
> kind of IO interface the VM needs.
>
> Best regards,
> Laszlo
>
> On Fri, Jan 20, 2017 at 10:21 PM, Wido den Hollander <wido@widodh.nl>
> wrote:
>
> > Hi,
> >
> > VirtIO SCSI [0] has been supported a while now by Linux and all kernels,
> > but inside CloudStack we are not using it. There is a issue for this [1].
> >
> > It would bring more (theoretical) performance to VMs, but one of the
> > motivators (for me) is that we can support TRIM/DISCARD [2].
> >
> > This would allow for RBD images on Ceph to shrink, but it can also give
> > back free space on QCOW2 images if quests run fstrim. Something all
> modern
> > distributions all do weekly in a CRON.
> >
> > Now, it is simple to swap VirtIO for VirtIO SCSI. This would however mean
> > that disks inside VMs are then called /dev/sdX instead of /dev/vdX.
> >
> > For GRUB and such this is no problems. This usually work on UUIDs and/or
> > labels, but for static mounts on /dev/vdb1 for example things break.
> >
> > We currently don't have any configuration method on how we want to
> present
> > a disk to a guest, so when attaching a volume we can't say that we want
> to
> > use a different driver. If we think that a Operating System supports
> VirtIO
> > we use that driver in KVM.
> >
> > Any suggestion on how to add VirtIO SCSI support?
> >
> > Wido
> >
> >
> > [0]: http://wiki.qemu.org/Features/VirtioSCSI
> > [1]: https://issues.apache.org/jira/browse/CLOUDSTACK-8239
> > [2]: https://issues.apache.org/jira/browse/CLOUDSTACK-8104
> >
>
>
>
> --
>
> EOF
>

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