On 04/15/2011 04:17 PM, Paolo Bonzini wrote: > On 04/15/2011 04:01 PM, Stefan Hajnoczi wrote: >> I think SCSI brings many benefits. Guests can deal with it better >> than these alien vdX virtio-blk devices, which makes migration easier. >> It becomes possible to attach many disks without burning through free >> PCI slots. We don't need to update guests to add cache control, >> discard, and other commands because they are part of SCSI. We can >> pass through more exotic devices. The list goes on... > > And we also have to reimplement all of MMC. :) > > A few questions: > > 1) Do you have anything posted for the virtio-scsi spec? I had started > working on one, but I haven't yet made it final. It included also > hotplug/unplug. I can send it out on Monday. > > 2) Have you thought about making scsi-disk and scsi-generic provide a > logical unit rather than a target? Otherwise passthrough of a whole > host or target becomes hard or messy. > > 3) Since I noticed Hannes is CCed, my next step for vmw_pvscsi would be > to dust off his patches to remove the bounce buffers, and see how they > apply to vmw_pvscsi. But I'd like to avoid duplicated work if possible. >
Argl. Why vmw_pvscsi? Any paravirtualized driver doesn't improve the situation here; we still wouldn't have a driver for unmodified guests. So either emulate existing drivers (like megasas :-) or go the full route and do a proper virtio-scsi. As for the bounce buffers thing: Good luck. Paul Brook absolutely insists on having them, but they kill performance for any sane backend. And both are basically impossible to reconcile; tried it once but got pushed back. And after about the third attempt I gave up. Let me know if you have more luck here. But keep me in the loop for the virtio-scsi spec. I do have some ideas what needs to get in there. As I think hch has. Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage h...@suse.de +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: Markus Rex, HRB 16746 (AG Nürnberg)
