Issues with 99-179r1 "Hard Drive Self-Tests"

Ralph Weber ralphoweber at csi.com
Wed Jun 2 15:40:34 PDT 1999


* From the T10 Reflector (t10 at symbios.com), posted by:
* Ralph Weber <ralphoweber at csi.com>
*
Mark,

I have a couple of big problems and a couple of nits with
the Hard Drive Self-Tests proposal (T10/99-179r1).

Big Problems:

1) The whole notion that a drive doing background self tests can
delay responses to regular commands for two seconds is going to
break the command timeout mechanism is most host device drivers.
Most host drivers timeout commands for which responses have not
been received in 30 seconds (sometimes less).  If the device
really takes 2 minutes, there are going to be command timeouts
(and probably bus resets) flying all over the place.

The only fix I can think of, short of changing host software,
is returning BUSY status.

2) While my opinion is not cast in stone, I'm really worried
about the changes to REQUEST SENSE.  I admit that REQUEST SENSE
looks like a convenient place to put this progress indication
feature.  But, selecting a REQUEST SENSE behavior based on a
bit in the CDB is a really big change.  At a minimum, lots more
band aids will have to be applied to the REQUEST SENSE definition
text.  Also, the proposed text:

   "When STPI is zero the device server shall not return the
   PROGRESS INDICATION field."

breaks the heck out of returning progress indications for FORMAT
commands.

Lastly, I'm wondering if anybody has considered the interactions
between these changes and RBC.

Options appear to be making these changes fit the current REQUEST
SENSE progress indication model (i.e., working without the new CDB
bit), or putting the progress indication in the log page, which will
be bad for RBC disks because RBC doesn't have log pages.

Nits:

3) The ASC/ASCQ mentioned in the second paragraph of 3.2 must be changed
to match the one shown in note 3 of table 4.

4) The last sentence before clause 7 needs to be clarified:

   "When the IMMED bit is set to one and the self-test routine
   fails, the device server shall log the self-test results and
   shall create a deferred error."

4a) Does 'log the self-test results' refer to the log page?  If
yes, specific details (or a pointer to already written specific
details) should be added.

4b) Is it possible or necessary to provide guidance on the
sense key and additional sense information to be provided in
the deferred error the device server is required to create?

Thanks.

Ralph...





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