Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support

[Paul Brook]

On Wednesday 29 April 2009, Christian Borntraeger wrote:
> Am Wednesday 29 April 2009 13:11:19 schrieb Paul Brook:
> > On Wednesday 29 April 2009, Christoph Hellwig wrote:
> > > On Tue, Apr 28, 2009 at 11:37:01AM -0500, Anthony Liguori wrote:
> > > > Ah, excellent.  I think that's a great thing to do.  So do you think
> > > > virtio-scsi would deprecate virtio-blk?
> > >
> > > I don't think so.  If you have an image format or a non-scsi
> > > blockdevice underneath virtio-block avoids the encoding into SCSI CDBs
> > > and back and should be faster.
> >
> > Is this actually measurably faster, or just infinitesimally faster in
> > theory?
>
> If the underlying backing is 4k block size and the emulated scsi disk has
> 512 byte block size, write performance can be a lot slower.

Rubbish. If this is really a problem you can just use a scsi disk with 4k 
sectors.

Paul