SPC-4: Late letter ballot comment READ ATTRIBUTE

Patrick Kiebach Patrick.Kiebach at quantum.com
Thu Apr 11 09:32:45 PDT 2013


Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1304110_f.htm">HTML-formatted message</a>

TYPO:
<<The READ ATTRIBUTE command shall be terminated with CHECK CONDITION status,
with the sense key set to MEDIUM ERROR, and the additional sense code set to
LOGICAL UNIT NOT READY, AUXILIARY MEMORY NOT ACCESSIBLE is if the cache bit
is set to one and the device server does not have a cache of attribute
information read from the most recently mounted medium and the medium
auxiliary memory is not accessible.>>
For this combination:
  1.  cache=1b:
     *	 Medium present but MAM is not accessible:
	*   cached attribute information exists;
The response should be GOOD status with attributes returned.
It sounds like a medium is loaded, the MAM is not available AND the cached
attribute data from a previous medium load is being returned.  I am not sure
that is a good idea.  But maybe that is what this statement is addressing:
==== Explanation ====
Since the requirement is "shall clear cached attribute information at the
start of a medium load" it is possible, even if cache=1b, to have no cached
attributes when medium is present and MAM is not accessible.  This would be
during the first part of the load.  This case was previously ignored when the
cache bit was brought in.
I like the idea of a table, but maybe look at it like this:
Medium not present
     Cache=0b
a. Cached MAM accessible   => NOT READY, MEDIUM NOT PRESENT
b. Cached MAM inaccessible => NOT READY, MEDIUM NOT PRESENT
     Cache=1b
a. Cached MAM accessible   => GOOD status, attributes returned
b. Cached MAM inaccessible => NOT READY, MEDIUM NOT PRESENT
Medium present
     Cache=0b
a. MAM accessible   => GOOD status, attributes returned
b. MAM inaccessible => MEDIUM ERROR
MAM Condition -
I.	Not operational => AUXILIARY MEMORY READ ERROR
II.    Not accessible  => AUXILIARY MEMORY NOT ACCESSIBLE
     Cache=1b
	  This bit ignored as medium is present, see above Medium present,
cache=0b.
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Kevin D Butt
Sent: Friday, March 29, 2013 10:42 AM
To: T10 Reflector; curtis.ballard at hp.com; Paul Suhler; Dennis Appleyard
Subject: SPC-4: Late letter ballot comment READ ATTRIBUTE
I have noticed an issue with SPC-4 READ ATTRIBUTE command and the new CACHE
bit. The definition seems to be incomplete and misses the case where
cache=1b, the medium is present but there is no attribute data cached.
I am requesting a late letter ballot comment to address this issue of
cache=1b, MAM inaccessible, and not attribute information is cached.
SPC-4 in the beginning of the READ ATTRIBUTE command should be modified to
read:
If the medium is present<< and the cache bit is set to zero>> but the medium
auxiliary memory is not accessible, the READ ATTRIBUTE command shall be
terminated with CHECK CONDITION status, with the sense key set to MEDIUM
ERROR, and the additional sense code set to LOGICAL UNIT NOT READY, AUXILIARY
MEMORY NOT ACCESSIBLE.
If the medium auxiliary memory is not operational, the READ ATTRIBUTE command
shall be terminated with CHECK CONDITION status, with the sense key set to
MEDIUM ERROR, and the additional sense code set to AUXILIARY MEMORY READ
ERROR.
and in the description of the CACHE bit:
A CACHE bit set to one specifies that, if medium is not present, then the
device server may report attribute information cached from the most recently
mounted medium. A CACHE bit set to zero specifies that the device server
shall not report attribute information cached from the most recently mounted
medium. The READ ATTRIBUTE command shall be terminated with CHECK CONDITION
status, with the sense key set to NOT READY, and the additional sense code
set to MEDIUM NOT PRESENT if the CACHE bit set to:
a) zero, and medium auxiliary memory is not accessible because there is no
medium present; or
b) one, and the device server does not have a cache of attribute information
read from the most recently mounted medium <<and the medium is not present>>.
<<The READ ATTRIBUTE command shall be terminated with CHECK CONDITION status,
with the sense key set to MEDIUM ERROR, and the additional sense code set to
LOGICAL UNIT NOT READY, AUXILIARY MEMORY NOT ACCESSIBLE is the cache bit is
set to one and the device server does not have a cache of attribute
information read from the most recently mounted medium and the medium
auxiliary memory is not accessible.>>
If medium is mounted and the CACHE bit is supported, then <<attribute
information shall be reported for the mounted medium and >>the CACHE bit
shall be ignored.
Attribute information from cache may or may not be the complete set of
attribute information from the most recently mounted medium. The device
server shall clear cached attribute information at the start of a medium
load.
==== Explanation ====
Since the requirement is "shall clear cached attribute information at the
start of a medium load" it is possible, even if cache=1b, to have no cached
attributes when medium is present and MAM is not accessible.  This would be
during the first part of the load.  This case was previously ignored when the
cache bit was brought in.
The unique conditions are:
  1.  cache=0b:
     *	 Medium not present:
	*   cached attribute information exists;
The response should be NOT READY, MEDIUM NOT PRESENT
	*   cached attribute information does not exist;
The response should be NOT READY, MEDIUM NOT PRESENT
     *	 Medium present but MAM is not accessible:
	*   cached attribute information exists;
The response should be MEDIUM ERROR, LOGICAL UNIT NOT READY AUXILIARY MEMORY
NOT ACCESSIBLE
	*   cached attribute information does not exist;
The response should be MEDIUM ERROR, LOGICAL UNIT NOT READY AUXILIARY MEMORY
NOT ACCESSIBLE
     *	 Medium present but MAM is not operational
The response should be MEDIUM ERROR, AUXILIARY MEMORY READ ERROR
  1.  cache=1b:
     *	 Medium not present:
	*   cached attribute information exists;
The response should be GOOD status with attributes returned.
	*   cached attribute information does not exist;
The response should be NOT READY, MEDIUM NOT PRESENT
     *	 Medium present but MAM is not accessible:
	*   cached attribute information exists;
The response should be GOOD status with attributes returned.
	*   cached attribute information does not exist;
The response should be MEDIUM ERROR, LOGICAL UNIT NOT READY AUXILIARY MEMORY
NOT ACCESSIBLE
<<Note that this case is not specified in the standard, but is what logically
follows>>
     *	 Medium present but MAM is not operational
The response should be MEDIUM ERROR, AUXILIARY MEMORY READ ERROR
Kevin D. Butt
SCSI & Fibre Channel Architect, Tape Firmware
Data Protection & Retention
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com
http://www-03.ibm.com/servers/storage/



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