RE: SCSI URL scheme [WAS: Re: iSCSI: 2.2.6. Naming & mapping]

[Howard Green <hgreen@Brocade.COM>]

I know that the following is kind of a radical question to ask, but has the time arrived to toss out LUNs as a means of identifying logical units, in favor of simply using the logical units' WWNs directly?

Currently, an IU containing a SCSI command identifies the target logical unit by a Logical Unit Number. Back in the good ol' days, LUNs were small integers contained directly in each CDB, and were (in practice, if not in theory) a simple index assigned to a specific logical unit throughout its life. 

SCSI has obviously evolved to a far more sophisticated state of affairs. The LUNs have grown to 64 bits, opaque used to identify a logical unit can vary over time, relative to the interface used, and as a function of the initiator's identity. 

The WWNs I've seen used to identify logical units currently range from 64 to 128 bits, 

> -----Original Message-----
> From: Raghavendra Rao [mailto:jpr@divyaroot.India.Sun.COM]
> Sent: Tuesday, October 03, 2000 10:56 AM
> To: ips@ece.cmu.edu
> Subject: Re: SCSI URL scheme [WAS: Re: iSCSI: 2.2.6. Naming & mapping]
> 
> 
> 
> > out-of-band).  I don't see the point of the initiator 
> sending its "view" to
> > the target at any point.  If the initiator sends an 
> incorrect view, you've
> > just created an error scenario which needs additional definition.
> 
> Well, to extend what Julian said further, the initiator could 
> ask the target
> for a LUN value corresponding to a WWN as part of the 
> authentication process,
> instead of presenting its view - whether right or wrong. But 
> something like
> this needs to be done as there is no easier/faster way to 
> translate a LU WWN
> to a LUN value.
> 
> This may also help in building an authentication method for a 
> LU access where
> no such thing exists today ?
> 
> 
> > case, the target will send its "view" for that initiator in 
> REPORT LUNS
> > SCSI command after login (which is actually the layer that 
> cares about the
> > LUN Map at all anyway).
> > 
> 
> This will be a problem if the storage controller has a lot of 
> LUNs. Since
> REPORT LUNS only returns a list of LUNs, the initiator still 
> has to send an
> INQUIRY (page 83) request to each LU to to find a matching LU 
> WWN (or until
> a matching WWN is found).
> 
> -JP
>