Re: [RFC PATCH 35/35] Add Xen virtual block device driver.

Rusty Russell
2006-03-25T10:03:11Z

On Fri, 2006-03-24 at 15:55 +0000, Alan Cox wrote:
> On Gwe, 2006-03-24 at 07:38 -0500, Jeff Garzik wrote:
> > > A pure SCSI abstraction doesn't allow for shared head scheduling which
> > > you will need to scale Xen sanely on typical PC boxes.
> >
> > Not true at all. If you can do it with a block device, you can do it
> > with a SCSI block device.
>
> I don't believe this is true. The complexity of expressing sequences of
> command ordering between virtual machines acting in a co-operative but
> secure manner isn't as far as I can see expressable sanely in SCSI TCQ

I thought usb_scsi taught us that SCSI was overkill for a block
abstraction? I have a much simpler Xen block-device implementation
which seems to perform OK, and is a lot less LOC than the in-tree one,
so I don't think the "SCSI would be better than what's there" (while
possibly true) is valid.

Cheers!
Rusty.
--
ccontrol: http://ozlabs.org/~rusty/ccontrol