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SubjectRe: iSCSI support for Linux



On Tue, 30 Oct 2001, Ashish A. Palekar wrote:

> Nitin:
>
> The Target side does support 64 bit LUNs - as recommended by SAM-2. The
> SCSI Target Mid-level definition for a LUN is a u64. (Note: The SCSI
> Target Mid-Level is a completely different entity than the SCSI
> Initiator Mid-Level). The question that is up in the air is how to use
> those 64 bits for a good target representation.

IIRC the top 2 bits of the first byte of the 8 byte lun define the layout-
this is what you have to look at on the initiator side when you do a REPORT
LUNS command.

>
> The other thing is that 64 bit LUNs are __VERY_RARELY__ used in the SCSI
> world that I am familiar with. So unless you are in a highly specialized
> operation where all 64 bits are important to you, you can get by with 32
> bit LUNs.
>

I'm not sure I agree. As we move into more and more virtualization types of
enviroments, the full 64 bit WWPN is often used as the 'lun'. So while it is
true that it's not important now, I suspect in a couple of years it might be.


> On the Initiator side, the LUN issue also needs to be addressed by the
> SCSI Initiator Mid-Level. The person to speak to in this regard would be
> Eric Youngdale (eric@andante.org). In fact the LUN issue along with the
> scan code are some of things on the SCSI todo list - the scan thing
> being especially important if you are doing fibre channel to enable
> dynamic target discovery.
>
> Hope this helps
> Ashish
>
> Nitin Dhingra wrote:
> >
> > Ashish,
> > I have seen your and other codes as well, I see that everybody's
> > used lun field as supplied by
> > middle layer right. No one is using 64-bit field acc. to SAM-2, but Linux
> > Scsi Subsystem doesn't support 64-bit
> > field it supports only 32-bit. Have you thought something about it and do
> > you have any solution to this?
> >
> > Kindly cc me as I am no longer in the mailing list.
> >
> > regards,
> > nitin
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