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Re: [Xen-devel] [PATCH 0/6] pvSCSI (SCSI pass through) driver

Hi James-san,

On Fri, 2 Nov 2007 11:23:50 +1100
"James Harper" <james.harper@xxxxxxxxxxxxxxxx> wrote:

> > Hi,
> > 
> > On Tue, 2007-10-30 at 19:39 +0900, Jun Kamada wrote:
> > 
> > Is this using the same syntax for HBA reservation that we used to
> have,
> > ie. simply enumerated using the scsi host number on the dom0?
> > 
> > If so, that is rather fragile.  The scsi host number can change from
> > kernel to kernel depending on HBA driver probe order and PCI bus
> > enumeration order.  It changes when hardware is rearranged.  And how
> do
> > we deal with migrate, when we'll need to select a completely different
> > HBA on a different host?
> > 
> > Selecting the HBA by scsi host number is good enough for a
> demonstration
> > that the code works, but I don't think it's going to be robust enough
> > for production deployment.
> > 
> > Also, has there been any progress towards exposing individual LUNs to
> > the guest rather than a whole HBA?
> People keep saying individual LUN... do they actually mean SCSI Target
> devices? Splitting up devices on the same HBA should be reasonably
> simple, but due to the way the scsi protocol works (AFAIK), splitting up
> LUN's on a single SCSI device could be a bit trickier...

The reason why we have to support SCSI on guest domain is that we would
like to use commercial appilications.
My understanding is as follows.

1.) There is a vender specific area in SCSI command frame. 
2.) There is a case that some data in the area depends on SCSI-ID, and
    some storage management software uses tha data. And sometimes the
    software requires one-to-one bindings to HBA. (This fuct is not good
    for standardization point of view.)

Possible solution may be 

a.) Assign a physical HBA for the guest domain the software, described
    in 2.), is running. And also multiple guest domains can share one
    physical HBA by using NPIV technology in this case.
b.) Assign LUNs for the other guests.

> Or maybe LUN doesn't mean what I think it means in this case... my
> understanding is:
> HBA = Host Bus Adapter (eg a PCI SCSI adapter)
> SCSI Target Device = one of the physical devices that sits on the SCSI
> bus (eg a tape drive or a disk drive)
> LUN (Logical Unit Number) = a sub unit of the SCSI Target Device, eg a
> single disk drive in a RAID array, a tape device in an multi tape drive
> autoloader, a CD ROM in a CDROM tower.

My understanding is same as yours.

Best regards,

Jun Kamada

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