Meaning of the PMI bit in the SCSI READ CAPACITY command -


i'm looking @ sbc-3 item 5.15 (read capacity (10) command). description of pmi bit (bit 0 of byte 8 in cdb) copied below:

"a pmi bit set 1 specifies device server return information on last logical block after specified in logical block address field before substantial vendor specific delay in data transfer may encountered."

my questions:

  • if both pmi bit , logical block address (bytes 2-5 in cdb) aren't zero, should (as target) still report last lba on disk?
  • if not above, should reported in case?
  • what should logical block address (bytes 2-5) value when pmi bit set?

(i know, pmi bit became obsolete in sbc-4, still need implement functionality according current standard)

this out in sbc-3 now, of revision 28 (january, 2011) can see change here: (sign required) http://www.t10.org/cgi-bin/ac.pl?t=d&f=11-010r0.pdf . so, you're talking sbc-2 compatibility.

anyway, don't think you'll ever see these fields set in practice. but, sake of completeness, may wish incorporate additional error handling.

  1. fail request if pmi zero, initiator specified lba.
  2. fail request if lba specified in cdb greater last lba of disk.

presuming implementation knows capacity of disk is, there should never "substantial vendor specific delay". can read standard, then, "return information on last logical block after specified in logical block address field". should last lba of disk.

to answer questions directly: when pmi set, , lba specified, should report last lba on disk, subject above error handling. and, need @ lba field error handling.


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