Report LUNs if more than 256 LUNs on the same bus

Elliott, Robert (Server Storage) Elliott at hp.com
Wed Apr 2 09:23:12 PDT 2008


* From the T10 Reflector (t10 at t10.org), posted by:
* "Elliott, Robert (Server Storage)" <Elliott at hp.com>
*
1. SAM-4 section 4.7.5 has specific "should" and "may" level recommendations
on which formats to use:
"If a SCSI target device contains 256 or fewer logical units, none of which
are dependent logical units (see
4.5.19.4), then the SCSI target device's LUNs:
a) should have the format shown in table 3 (i.e., peripheral device
addressing);
b) may have the format shown in table 4 (i.e., flat space addressing); or
c) may have the format shown in table 5 (i.e., extended flat space
addressing).
If a SCSI target device contains more than 256 logical units and 16 384 or
fewer logical units, none of which are
dependent logical units (see 4.5.19.4), then the SCSI target device's LUNs:
a) should have the format shown in table 4 (i.e., flat space addressing);
b) may have the format shown in table 5 (i.e., extended flat space
addressing); or
c) may have the format shown in table 3 (i.e., peripheral device addressing)
for up to 256 of the logical units
within SCSI target device.
If a SCSI target device contains more than 16 384 logical units, none of
which are dependent logical units (see
4.5.19.4), then the SCSI target device's LUNs:
a) should have the format shown in table 5 (i.e., extended flat space
addressing);
b) may have the format shown in table 4 (i.e., flat space addressing) for up
to 16 384 of the logical units
within SCSI target device; or
c) may have the format shown in table 3 (i.e., peripheral device addressing)
for up to 256 of the logical units
within SCSI target device."
2. The byte order suggested in the original email is wrong.  Using this
example:
"40 00 00 00 00 00 00 00 to 40 00 00 00 00 00 3F FF for all the LUNs"
all the non-zero bits should be together at the front:
40 00 00 00 00 00 00 00 to 7F FF 00 00 00 00 00 00
Meaning:
  address method (2 bits) 01b
  flat-space LUN values (14 bits) 0000h to 3FFFh
---
Rob Elliott (elliott at hp.com)
HP Industry Standard Server Storage Advanced Technology
---
Rob Elliott (elliott at hp.com)
HP Industry Standard Server Storage Advanced Technology
-----Original Message-----
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of
Gerry.Houlder at seagate.com
Sent: Tuesday, April 01, 2008 10:32 AM
To: Marian_Lakov at us.xyratex.com
Cc: t10 at t10.org
Subject: Re: Report LUNs if more than 256 LUNs on the same bus
* From the T10 Reflector (t10 at t10.org), posted by:
* Gerry.Houlder at seagate.com
*
There are some options on this. Please refer to SAM-4, clause 4.7 for a
full description on this. My opinions listed here:
(a) You could use peripheral device addressing method, where 2 most
significant bits of byte 0 are set to 00 binary. This groups the LUNs on
different buses (6 bits of byte 0 consists of a bus identifier) with up to
256 LUNs per bus. The effective address space for this is
00 00 00 00 00 00 00 00 through 3F FF 00 00 00 00 00 00.
(b) You could use the flat space addressing method, where the 2 MS bits of
byte 0 are set to 01 binary.
This gives LUNs 40 00 00 00 00 00 00 00 through 7F FF 00 00 00 00 00 00.
 If this isn't enough for you, you need to use the multilevel structure
defined later in the clause. If you need that much space, you definitely
need to read SAM-4.
	     "Marian Lakov"
	     <Marian_Lakov at us.
	     xyratex.com>						To
	     Sent by:		       <t10 at t10.org>
	     owner-t10 at t10.org						cc
	     No Phone Info
	     Available						   Subject
				       Report LUNs if more than 256 LUNs
				       on the same bus
	     03/31/2008 03:38
	     PM
Hi,
If a RAID controller presents more than 256 LUNs to a host on the same bus
what is the proper LUN format?
00 00 00 00 00 00 00 00 to 00 00 00 00 00 00 00 FF for the LUNs 0 to 255
and
40 00 00 00 00 00 01 00 to 40 00 00 00 00 00 3F FF for the LUNs above 255
or
40 00 00 00 00 00 00 00 to 40 00 00 00 00 00 3F FF for all the LUNs
Also, for the LUNs above 255, is it possible to use 00 00 00 00 00 00 01 00
to 00 00 00 00 00 003F FF format?
Thanks,
Marian
________________________
Marian Lakov
Systems Engineer
Xyratex
1804 Centre Point Circle, Suite #112
Naperville, IL 60563
Office:  630-364-7600
Fax:	 630-364-7601
marian_lakov at us.xyratex.com
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