LongLBA bit in READ CAPACITY (10) command
Pat LaVarre
LAVARRE at iomega.com
Wed Oct 2 05:57:25 PDT 2002
* From the T10 Reflector (t10 at t10.org), posted by:
* "Pat LaVarre" <LAVARRE at iomega.com>
*
Trying op x25 ReadCapacity10 before resorting to ReadCapacity16 might only work for awhile?
Already we have Windows with motherboards that in combination can't copy anything but multiples of 4 bytes e.g. http://members.aol.com/plscsi/20020328/oddwinme.txt
How long will it be before we have hosts that can't copy anything but multiples of 16 bytes? Op x25 ReadCapacity10 implicitly involves copying in just 8 bytes.
Before then, we'll see the popular op x12 Inquiry for x24 bytes choke. I wonder if that's popular enough to keep people from building hosts that can't copy anything but multiples of 8 bytes.
Pat LaVarre
P.S. Thanks to Robert E for the education re ReadCapacity16 etc.: me, I haven't yet been paying much attention to disk capacities above 2 TiB @ 0.5KiB/block.
-----Original Message-----
From: Elliott, Robert (Server Storage) [mailto:Elliott at hp.com]
Sent: Mon 9/30/2002 8:27 PM
To: t10 at t10.org
Cc:
Subject: RE: LongLBA bit in READ CAPACITY (10) command
* From the T10 Reflector (t10 at t10.org), posted by:
* "Elliott, Robert (Server Storage)" <Elliott at hp.com>
*
Sorry for the delay in responding. The most recent changes to the READ
CAPACITY command are described in T10 proposal 01-246r1, accepted for
SBC-2 revision 5.
The LONGLBA bit in READ CAPACITY(10) was removed in favor of a READ
CAPACITY(16) command. It used to request the long vs. short format
data. READ CAPACITY(10) now just returns the short format, with a value
of FFFFFFFFh if the capacity is too large to express. If you get
FFFFFFFFh, you have to run READ CAPACITY(16) and parse the long format
data.
The description of LONGLBA was removed but the bit was left in Table 31
through SBC-2 revision 7; I will remove it from SBC-2 revision 8 (posted
by the November T10 week).
---
There are lots of ingredients to the discovery process, some protocol
and command set specific. Some things you'll encounter:
Protocols:
SPI-n: negotiation
SPI-3 Ultra 160 SCSI: Domain validation (INQUIRY, READ BUFFER, WRITE
BUFFER) to pick correct speed
SPI-4 Ultra 320 SCSI: Read INQUIRY to decide to enable information units
and QAS
Serial Attached SCSI: Program expander routing tables
Command sets:
Disk drives: Long LBAs, check mode pages
Tape drives: implicit vs. explicit LBA modes, ensure mode pages are
correct
Multimedia: features
General:
Well-known LUNs (try the REPORT LUNS W-LUN first?)
new sense data format
persistent reservations (are you always ready for RESERVATION CONFLICT)
access controls
target port groups
determine what optional commands/task management functions are available
identify LUs only by their VPD data; support multiple paths
I agree that the different (sometimes inexplicably) discovery sequencing
across OSes has been a problem, and would welcome an informative annex
proposals for SBC-2 that would help this. SBC-2 would only cover step 3
in your list (probing a disk device); finding the LUs themselves is not
disk specific (suitable for an annex in SPC-3).
--
Rob Elliott, elliott at hp.com
Industry Standard Server Storage Advanced Technology
Hewlett-Packard
...
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