SSC-4: Medium partition mode page and differences between mode select and mode sense
Kevin D Butt
kdbutt at us.ibm.com
Tue Nov 24 11:52:53 PST 2009
Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r0911240_f.htm">HTML-formatted message</a>
Tape guru's,
I have been looking at the Medium Partition mode page (11h) in SSC-4. In
the definition of PARTITION SIZE fields I am trying to determine what the
difference is between these fields in a Mode Select command vs. a Mode
Sense command.
The text that follows in magenta seems to allow a less than desired
implementation. In fact, it seems to conflict the intent of Note 70. If
the device server is reporting sizes of partitions, why would it not chose
to set the PSUM and PARTITION UNITS fields such that the partition sizes
can be represented? I think that when the PARTITION UNITS field was
added, this sentence should have been removed.
I have attempted to modify the text from SSC-4 by adding the text in green
(and suggesting that the text in magenta should be deleted).
PARTITION SIZE fields within the partition size descriptor list define the
approximate size of the respective partitions in the units specified in
the PSUM and PARTITION UNITS fields. Partitions are numbered by their
relative position in the partition size descriptor list, starting at 0.
Only partition numbers in the range of 0 to n where n is less than or
equal to 63 may have size descriptors in this mode page. Partition n, if
present, shall be described by the partition size descriptor at mode page
offsets 8+(2*n) and 9+(2*n). Partition 0 shall be the default partition.
Partition size descriptor 0, shall contain the size of the default
partition. The size of partition 0 shall be greater than 0. Up to 64
partitions may be defined using this mode page. Partitions not assigned
shall have a partition size descriptor of 0. The logical unit may support
more partitions than partition size descriptors. A logical unit may
support more partition size descriptors than supported by the volume. All
partition size descriptors representing a partition number greater than
the maximum additional partition count shall be 0. The partition size
descriptors are undefined if the logical unit is not ready. A MODE SELECT
command partition size descriptor of FFFFh requests that the logical unit
allocate all remaining partition space to that partition. A MODE SENSE
command shall return a partition size descriptor of FFFFh if the partition
size, in units of PSUM or PARTITION UNITS, is greater than or equal to
FFFFh. If insufficient space exists on the volume for the requested
partition sizes or if multiple partition size descriptors are set to
FFFFh, the device server shall return CHECK CONDITION status. The sense
key shall be set to ILLEGAL REQUEST and the additional sense code shall be
set to INVALID FIELD IN PARAMETER LIST. A device server may round, as
described by the MODE SELECT command in SPC-4, any partition size to the
nearest valid partition size. When a MODE SENSE command is received after
a MODE SELECT command that had the POFM bit is set to zero but before a
FORMAT command the values in the PARTITION SIZE, PSUM, andPARTITION UNITS
fields shall be the values set by the MODE SELECT command. When a MODE
SENSE command is received, the logical unit is ready, and there is no
pending change related to a MODE SELECT command for this page the PSUM,
and PARTITION UNITS fields and any PARTITION SIZE fields that are returned
shall reflect the size on the medium of the related partition.
NOTE 70 - It is recommended, but not required, that the number of
partition size descriptors available through the Medium Partition mode
page equal at least the number of maximum additional partitions + 1. This
provides a mechanism for the device server to disclose the current
partition sizes.
Does this sound correct and does it look like something that we should
attempt to clarify in SSC-4. If the answer is yes, I will prepare a
proposal to explicitly state the difference between Mode Select and Mode
Sense with and without a pending change.
Thanks,
Kevin D. Butt
SCSI & Fibre Channel Architect, Tape Firmware
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
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