SCSI/ATA Translation of Command Duration Limit (T10/15-093)
Paul.Suhler at hgst.com
Wed Jun 10 17:23:28 PDT 2015
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I would like to solicit opinions on how to do convert the command duration
limit times expressible in SCSI into the isochronous command completion (ICC)
times expressible in ATA. The problems are:
a) SCSI can express times as low as 1 microsecond, while ATA only goes down
to ten milliseconds.
b) SCSI can express times as large as 32k - 1 seconds, while ATA only goes
up to 64 seconds.
c) In some ranges of times, SCSI can express values with a finer granularity
that ATA can.
There are two possible solutions for the SATL:
a) Reject any MODE SELECT command that specifies a value that does not map
precisely to an ATA value; or
b) Round the SCSI value to the nearest ATA value.
Rounding (b) will allow the ATA device to make a best effort at setting a
command duration limit. On the other hand, the value used may be as much as
a factor of 10,000 larger than that specified (1 usec), or as little as
1/500th of that specified (32k-1).
I'll also note that neither ATA nor SCSI has a mechanism to report the actual
range of values supported by a particular device, and neither ACS-4 nor SPC-5
specifies what to do in case of an unsupported value.
Straw poll time. Vote early and vote often!
Paul A. Suhler, PhD
Research Staff Member
paul.suhler at hgst.com
3001 Daimler St.
Santa Ana, CA 92705-5812
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