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

[Christian Borntraeger]

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.