Command progress proposal for SPC

exabyte!smtplink!tedl at uunet.uu.net exabyte!smtplink!tedl at uunet.uu.net
Wed Nov 16 06:40:07 PST 1994


Determining the status of an immediate command     X3T10/94-244r0

To:       Membership of X3T10

From:     Edward Lappin
          Exabyte Corporation
          tedl at exabyte.com
          (303) 447-7718

Date:     November 15, 1994

Subject:  Determining the status of an immediate command


Background:

During the SSC discussion on 11/10/94, it was concluded that we
need a clarification on the definition of ready for sequential
devices (such as tape).  We agreed on the following rules:

1. If the volume is being mounted or unmounted, the logical
   unit shall return CHECK CONDITION to a TUR command, with an
   appropriate status (depends if unloading or loading).
   
2. If the volume is mounted, the logical unit shall return
   GOOD STATUS in response  to a TUR.
   
3. If the volume is not mounted, the logical unit shall
   return NOT READY  in response to a TUR.
   
Therefore, the processing of an immediate command (such as erase
immediate) will not change the ready status of the logical unit.
Because of this, another reporting mechanism is required to
determine if an immediate command is in progress and the
approximate stage of processing.

Proposal:

1. That a new ASC/ASCQ pair be added to SCSI-3 SPC.

ASC  ASCQ  DTLPWRSOMC      Description

00   16    DTLPWRSOMC      IMMEDIATE COMMAND IN PROGRESS

2. That the Sense-key specific section of Request Sense in SCSI-
   3 SPC be amended to change the text for the progress
   indication bytes.

Old text:
   If the sense key is NOT READY and the SKSV bit is one, the
   sense-key specific field shall be as shown in table 45.
   These fields only apply to the FORMAT UNIT command with the
   Immed bit set to one.

New text:
   If the sense key is NOT READY or NO SENSE and the SKSV bit is
   one, the sense-key specific field shall be as shown in table
   45.

Old table caption:
   Table 45 - Format progress indication bytes

New table caption:
   Table 45 - Progress indication bytes

Notes:

1. This change removes the requirement that the FORMAT UNIT
   immediate command change the ready status to NOT READY.  If
   needed, this requirement can be stated in SBC.

2. Any ASC/ASCQ may report a progress indication if the sense
   key is NOT READY.  However, to make sense, the progress
   indication should only be used if there is progress to
   report, such as progress towards ready, or possibly, progress
   towards completion of the not ready (such as unloading a
   tape).

3. Any ASC/ASCQ may report a progress indication if the sense
   key is NO SENSE.  This change allows a device to support the
   reporting of relative progress for any command without
   changing the ready status of the device.  Currently, I
   believe that only immediate commands would report a progress
   indication with NO SENSE but I do not believe we should
   restrict this reporting if a device wishes to support it.  If
   no command is in progress and there is no expected change in
   the ready state of the device, the SKSV bit shall be 0.

4. The use of the ASC/ASCQ of LOGICAL UNIT NOT READY, FORMAT IN
   PROGRESS would still be used if the logical unit reports NOT
   READY.  If the logical unit reports READY, the ASC/ASCQ of
   IMMEDIATE COMMAND IN PROGRESS should be used instead.

5. It is the intent of this change to allow an initiator to poll
   the logical unit with REQUEST SENSE to determine if the
   immediate command has completed, and if supported, determine
   the progress of the command.  Polling with TUR will not work
   since the logical unit is ready (though it is not guaranteed
   to be able to queue or process the command).  It is not the
   intent of this change to report CHECK CONDITION on a TUR
   command while an immediate command is in progress.




More information about the T10 mailing list