On 08/04/2010 11:48 AM, Alexander Graf wrote:
On 04.08.2010, at 18:46, Anthony Liguori wrote:
On 08/04/2010 11:44 AM, Avi Kivity wrote:
On 08/04/2010 03:53 PM, Anthony Liguori wrote:
So how do we enable support for more than 20 disks? I think a virtio-scsi is inevitable..
Not only for large numbers of disks, also for JBOD performance. If you have one queue per disk you'll have low queue depths and high interrupt rates. Aggregating many spindles into a single queue is important for reducing overhead.
Right, the only question is, to you inject your own bus or do you just reuse SCSI. On the surface, it seems like reusing SCSI has a significant number of advantages. For instance, without changing the guest's drivers, we can implement PV cdroms or PC tape drivers.
What exactly would keep us from doing that with virtio-blk? I thought that supports scsi commands already.
I think the toughest change would be making it appear as a scsi device
within the guest. You could do that to virtio-blk but it would be a
flag day as reasonable configured guests will break.
Having virtio-blk device show up as /dev/vdX was a big mistake. It's
been nothing but a giant PITA. There is an amazing amount of software
that only looks at /dev/sd* and /dev/hd*.
Regards,
Anthony Liguori
Alex
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