Re: iSCSI - structured values

[Keith McCloghrie <kzm@cisco.com>]

I think the issue is that multiple assignments within a 16-bit
identifier assume that there is coordination between the various
components that need to make/use those assignments for the same iSCSI
instance.  Obviously, that is true if the components will share the
same assignment.  However, the expansion beyond 16-bits for ISID
recognizes that such coordination is not possible in all cases in
Initiators.  I suggest that even if one can not see it today, we
should not prohibit future innovation which could well create the
same problem for Target Portal Groups.

Furthermore, it is now apparent that the proposed resolution of the
problem for Initiators punts the problem to vendors.  That is, the WG
is requiring vendors to implement a proprietary mechanism in order to
have interoperability between two different products from the same
vendor.  I'm very doubtful that is kosher.

Keith. 

> What is the problem you would like to solve by applying the same scheme to
> assigning Target Portal Group numbers?  The problem of ISID assignment was
> different than Target Portal Group number assignment.  Since I don't see a
> similar problem with targets and their portal group assignment, I don't see
> the need for changes regarding TPG numbering.
> 
> Marjorie
> 
> > -----Original Message-----
> > From: Keith McCloghrie [mailto:kzm@cisco.com]
> > Sent: Wednesday, December 05, 2001 9:23 AM
> > To: ips@ece.cmu.edu
> > Cc: kzm@cisco.com
> > Subject: iSCSI - structured values
> > 
> > 
> > Hi,
> > 
> > The following ideas came up in a discussion I had about iSCSI.
> > 
> > The first issue is about the algorithm to use for allocating the
> > structured ISID values, which contain three fields:
> > 
> >  - The Type field identifies the format:
> >            00h     - IEEE OUI
> >            01h     - IANA Enterprise Number (EN)
> >            02h     - "Random"
> >            03h-FFh - Reserved
> >  - The Naming Authority field identifies the vendor or organization
> >  - The Qualifier field is a 16 bit value that provides a range of
> >    possible values for the ISID within the Type and Naming Authority
> >    namespace.
> > 
> > The "notes" in draft-ietf-ips-iscsi-name-disc-03.txt specify:
> > 
> >      (a) As noted, the structure of the ISID namespace provides each
> >      vendor with its own piece of the ISID namespace.  In effect, this
> >      provides for a vendor-partitioning of that namespace within each
> >      initiator.
> > 
> > So, this puts the onus on a "vendor" to come up with the vendor's own
> > scheme for allocating ISID values.  For the situation where a vendor
> > wants to assign different values to different interfaces/HBAs, the
> > simplest scheme would be to use a unique value which is shipped with
> > each product, such as a MAC address.  This would be simple because it
> > would obviate any need to coordinate between different interfaces
> > (even those from the same vendor).  In fact, the first three bytes of
> > a 6-byte MAC address are an IEEE OUI, which is exactly what type=0
> > specifies, except that the MAC address has 3 more bytes, and the
> > Qualifier field is only 2 bytes.  So, in order to allow vendors to
> > adopt such a simple scheme, I'd like to propose that the Qualifier
> > field be enlarged to at least 3 bytes.  It probably doesn't make much
> > sense to make the overall ISID to be 7 bytes long.  So, how about
> > making the Qualifier be 4 bytes so that the ISID is 8 bytes long ?  
> > As far as I'm aware the performance impact of this is virtually
> > negligible, and so I can't really see any disadvantage in doing so.
> > 
> > The second issue concerns Portal Group Tags.  It seems that despite 
> > the difference in terminology, that an ISID and a Portal Group Tag
> > are corresponding concepts.  For example, a SCSI Port Name is defined
> > as "the iSCSI Name + 'i' or 't' + ISID or Portal Group Tag".  However,
> > a Portal Group Tag is defined as a 16-bit integer.  Now, I understand
> > that an ISID was originally defined as a 16-bit integer, before its
> > format was expanded (as discussed above).  So, with the correspondence
> > of ISID and Portal Group Tag, surely it makes sense for a Portal Group
> > Tag to have the same format as an ISID.  This will allow vendors of
> > iSCSI targets with multiple interfaces/HBAs to use a simple scheme as
> > and when they need to assign different Portal Group Tag values to the
> > different interfaces/HBAs.  So, whether or not the ISID format is
> > changed based on the first issue above, I propose that the same
> > structured format be used for both ISIDs and Portal Group Tags.
> > 
> > Keith.
> > 
>