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

[boutcher@xxxxxxxxxx (Dave C Boutcher)]

Jeff Garzik wrote:
>Arjan van de Ven wrote:
>> On Fri, 2006-03-24 at 08:37 -0500, Jeff Garzik wrote:
>>> Jeff Garzik wrote:
>>>> 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.
>>> Another benefit of SCSI:  when an IBM hypervisor in the Linux kernel 
>>> switched to SCSI, that allowed them to replace several drivers (virt 
>>> disk, virt cdrom, virt floppy?) with a single virt-SCSI driver.
>
>> but there's a generic one for that: iSCSI
>> so in theory you only need to provide a network driver then ;)
>
>Talk about lots of overhead :)
>
>OTOH, I bet that T10 is acting at high speed, right this second, to form 
>a committee, and multiple sub-committees, to standardize SCSI 
>transported over XenBus.  SXP anyone?  :)

Actually SRP (which T10 has now stopped working on) fits the bill very
nicely.

I have to say that moving the IBM virtual drivers from a random
collection of unique drivers (viodisk, viotape, viocd) to a single
virtual SCSI HBA made life much easier.

There is a group (actually, at least two groups) working on SCSI
target infrastructures...once that is in place, I would expect we
could start hacking a Xen virtual HBA.

We looked at iSCSI as a transport (instead of SRP) but we felt that 
the added complexity made it unlikely that the average human could
successfully boot their virtual machine

Dave B

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