Questions on relative target ports

Elliott, Robert (Server Storage) elliott at
Wed Mar 3 08:21:49 PST 2004

* From the T10 Reflector (t10 at, posted by:
* "Elliott, Robert (Server Storage)" <elliott at>

> -----Original Message-----
> From: owner-t10 at [mailto:owner-t10 at] On Behalf 
> Of Burn Alting
> Sent: Tuesday, March 02, 2004 5:11 PM
> Subject: Questions on relative target ports
> I am doing some work on raids and have some questions on 
> Relative Target Ports.
> Let's say I have a raid enclosure with two controllers, each of which
> has two host ports. I can configure a "data set of disks" to 
> present on one or more of the controllers and their host ports.
> Now my question is:- Is a 'relative target port identifier'
> a. with reference to the hardware (ie controller 0 port 0 == 0x01,
> controller 0 port 1 == 0x02, controller 1 port 0 == 0x03 and 
> controller 1 port 1 == 0x03)
> OR
> b. with reference to the data set (ie if the data set is 
> presented only on controller 1, port 1, then the relative target
> port identifier will be 0x01; alternately if it where on both 
> host ports on controller 1, then port 0 would be 0x00 and 
> port 1 would be 0x01).
> Thanks in advance
> -- 
> Burn Alting <burn at>

I'm not sure what you mean by "data set of disks."  SCSI defines
logical units, target ports, and target devices.

If there are 4 target ports providing access to the logical unit
(they're all in the same target device), they could be numbered:
controller 0 port 0: relative port identifier 1
controller 0 port 1: relative port identifier 2
controller 1 port 0: relative port identifier 3
controller 1 port 1: relative port identifier 4

If some logical units are only accessible through some target
ports due to configuration (e.g. the Access Controls commands), 
the relative port identifiers should still be consistent.  
Relative port 1 should refer to the same target port, regardless 
of which logical unit is being accessed.

If certain logical units are only accessible through certain
target ports forever, then they might need to be considered 
as being in two separate SCSI target devices.  

Rob Elliott, elliott at
Hewlett-Packard Industry Standard Server Storage Advanced Technology

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