Alan Cox wrote: > On Mer, 2006-03-22 at 18:09 -0500, Jeff Garzik wrote: >> An IBM hypervisor on ppc64 communicates uses SCSI RPC messages. I think >> this would be quite nice for Xen, because SCSI (a) is a message-based >> model, and (b) implementing block using SCSI has a very high Just >> Works(tm) value which cannot be ignored. And perhaps (c) SCSI target >> code already exists, so implementing the server side doesn't require >> starting from scratch, but rather simply connecting the Legos. > > 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. In fact, SCSI should make a few things easier, because the notion of host+bus topology is already present, and notion of messaging is already present, so you don't have to recreate that in a Xen block device infrastructure. > SCSI emulations > are also always full of bits people got wrong, often critical bits like > tagged queues and error sequences - things that break your journalled > file system. This I'll grant you. Jeff
