iscsi : changes involving tgt portal group tag.

Robert Snively rsnively at Brocade.COM
Wed Mar 13 09:34:02 PST 2002

In SCSI (and I presume in iSCSI), there is no requirement that
the logical unit number to logical unit mapping be the same as
seen by all ports.  In other words, it is a Port||LUN combination
that identifies a logical unit, not a LUN alone.  The mappings
can be determined by a number of discovery mechanisms and verified
by use of the logical units world-wide name identifier from the

I don't think this has much effect on the rest of the ongoing
discussion, but if it does, please keep it in mind.

> Part of the concern appears to be around the worry that an initiator
> might reconnect to "the wrong" port and as a result end up talking to
> the wrong LU when it issues additional commands to a LUN it knows.
> I don't understand how that's possible.  SAM-2 section 4.7.3 shows
> that an LU is a component of a Device (not of a Port).  And 4.8 says
> that a LUN "identifies the logical unit within a SCSI target device".
> In other words, no matter what port you use to access a device, a
> given LUN identifies the same LU in that device.

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