SAT definition of ARRE bit in mode page

Mark Overby MOverby at nvidia.com
Mon Feb 8 11:03:40 PST 2010


Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1002083_f.htm">HTML-formatted message</a>

The behavior you seek is vendor-specific (reassigning blocks on a read
recovery).
There is a write-and-verify feature. It is the write-read-verify feature set.
On 2/8/10 9:45 AM, "Bill.Martin at emulex.com" <Bill.Martin at emulex.com> wrote:
In SAT, it was determined during letter ballot resolution to make ARRE set to
zero and AWRE set to one in the Read-write error recovery mode page.  The
reasoning was as follows (from 06-121r5):
Discussed: What is the reasoning behind the specified values for ARRE and
AWRE? LB comments from HPQ and LSI as well as 05-241r2 suggest AWRE should be
"one", and ARRE should be "zero". My understanding is that an ATA device will
auto-reallocate on an unrecoverable READ error, but that the reallocation is
deferred until the next time that same logical sector is written. An ATA
device does not check data consistency on a write, and there is no
write-and-verify equivalent, so I don't see that an ATA device will
auto-reallocate due to an error on a write command. But..., the data that
ends up in the alternate sector is the data from the write, not the data from
the read, so AWRE is one and ARRE is zero.
This discussion is based around an unrecoverable read error; however from
SBC-3r21, ARRE is based on a recovered read error.  The following is from
6.4.5 Read-Write Error Recovery mode page:
An ARRE bit set to one specifies that the device server shall enable
automatic reassignment of defective logical blocks during read operations.
All error recovery actions required by the error recovery bits (i.e., the EER
bit, the PER bit, the DTE bit, and the DCR bit) shall be processed. The
automatic reassignment shall then be performed only if the device server
successfully recovers the data. The recovered data shall be placed in the
reassigned logical block. The device server shall report any failures that
occur during the reassignment operation. Error reporting as specified by the
error recovery bits (i.e., the EER bit, the PER bit, the DTE bit, and the DCR
bit) shall be performed only after completion of the  reassignment operation.
See the REASSIGN BLOCKS command (see 5.19) for error procedures.
This clearly states that the reassignment is ONLY performed if the device
server successfully recovers the data.
I am looking for clarification on how ATA devices operate.  If an ATA device
recovers read data will it reassign the block during the read operation to a
different location on the media?  If it will make this reassignment, then I
will bring in a proposal for SAT-3 to change the bit settings in this mode
page.
Bill Martin
Emulex
Office of Technology
Industry Standards
916 772-3658
916 765-6875 (Cell)
bill.martin at emulex.com
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