Review of proposal 09-038

Gerry.Houlder at seagate.com Gerry.Houlder at seagate.com
Fri Mar 13 07:24:57 PDT 2009


* From the T10 Reflector (t10 at t10.org), posted by:
* Gerry.Houlder at seagate.com
*
I reviewed Mark's proposal 09-038 and am in agreement with the changes
proposed. I can see that the intent is to make purely editorial changes.
I did see something not related to the changes that is really strange,
however. The last sentence in 4.19.1 reads:
"During background scan operation, the device server shall ignore pseudo
unrecovered error with correction disabled (see 4.14.2) and shall process
pseudo unrecovered errors with correction enabled."
Background scans should only ignore pseudo unrecovered errors. Scans should
not reassign or mark for future reassignment or even waste time performing
extensive recovery on such logical blocks. It seems dumb for every
background scan to log an unrecoverable read error for each pseudo
unrecovered error encountered, which is required when processing a pseudo
unrecovered error with correction enabled (see 4.14.2). I believe only the
"correction disabled" rules should apply to background scan handling of
pseudo unrecovered errors.
Its not obvious to me what is meant by "correction enabled" and "correction
disabled". There is a CORRCT bit is Read Long that has a description like
enabling or disabling correction, but this is not applicable to normal
reads or scans. The DCR bit in Mode page 1 is applicable to reads and
scans, but that bit specifies that ECC not be used for correction, only
rereads. This bit being set doesn't relieve the drive from attempting
recovery and logging/reporting any resulting errors, so even if set this is
more like the "with correction enabled" rules. It seems to me that the only
thing close to "with correction disabled" is when the CONT bit in Mode Page
1 is set,; this is intended for video applications and not used in typical
computer applications. In my opinion, only the CONT bit and the CORRCT bits
qualify is "correction disabled". What is your opinion on this?
I think some clarification is needed here, probably affecting text in
clause 4.14 as well as the sentence in 4.19.1 that caught my attention. I
don't think this issue should affect Mark's proposal, but the issue should
be discussed during CAP and a new proposal reflecting the group's definiton
of "with correction disabled". I will not be attending T10 meetings in
March. If the goup chooses to defer this item to May (when I expect to be
attending) that would be OK, but I would like to encourage discussion to
start at the March meeting.
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