SCSI/ATA Translation of Command Duration Limit (T10/15-093)

Gerry Houlder gerry.houlder at seagate.com
Thu Jun 11 07:21:52 PDT 2015


Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1506110_f.htm">HTML-formatted message</a>

Please remember that a true SCSI device probably doesn't support the entire
minimum to maximum range that is possible, and may not support resolution
down to 1 usec either. I don't remember what the T10 proposal specifies
(i.e., rounding or rejecting) but the SAT-3 behavior ought to be the same.
Also, are ATA devices required to handle the entire expressable range of
time, or is there an ATA mechanism for rejecting/ rounding out of range
values?
In the interest of friendliness to the host (i.e., making it as easy as
possible for a host to determine minimum and maximum acceptable times),
rounding is best. A CHECK CONDITION occurs when rounding happens, so the
host will be aware that the requested time was not acceptable and the
device has made best effort to implement its closest option.
On Wed, Jun 10, 2015 at 7:42 PM, Ralph Weber <Ralph.Weber at wdc.com> wrote:
>  As David Black would say at a time like this ... "With my chair's hat
> totally removed ..."
>
> Option b for times larger than 90 seconds and smaller than 1 millisecond
> Option a for all other conversions
>
> All the best,
>
> .Ralph
>  ------------------------------
> *From:* owner-t10 at t10.org [owner-t10 at t10.org] on behalf of Paul Suhler [
> Paul.Suhler at hgst.com]
> *Sent:* Wednesday, June 10, 2015 7:23 PM
> *To:* T10 E-mail Reflector (t10 at t10.org)
> *Subject:* SCSI/ATA Translation of Command Duration Limit (T10/15-093)
>
>   Hi, everyone.
>
>
>
> 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!
>
>
>
> Thanks,
>
>
>
> Paul
>
>
>
> *Paul A. Suhler, PhD*
>
> Research Staff Member
>
> HGST Research
> *paul.suhler at hgst.com <paul.suhler at hgst.com>*
> o: 949-757-3432
>
> m: 949-241-6443
>
> 3001 Daimler St.
> Santa Ana, CA 92705-5812
> www.hgst.com
>
>
>



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