[T10] WRITE SAME and 0 LBA counts

Black, David david.black at emc.com
Sun May 22 15:30:58 PDT 2016


> That said, however, it would appear that the two quoted SBC-4 text
> citations profoundly violate T10's "say it the same way everywhere"
> strong recommendation (i.e., rule).

Indeed they do ...

> Therefore ...
> 
> Although I cannot support adding "computed" anywhere, I see no reason
> why the SBC-4 editor cannot step in, pick a single phrase to describe
> the quantity, and cause that phrase to be used consistently.
> 
> In the event that the SBC-4 editor decides to solicit guidance from this
> reflector, my vote is for the wording with "contiguous" and "requested"
> in it.

I concur with this suggestion.

Thanks, --David

> -----Original Message-----
> From: t10-bounces at t10.org [mailto:t10-bounces at t10.org] On Behalf Of Ralph
> Weber
> Sent: Saturday, May 21, 2016 7:34 AM
> To: t10 at t10.org
> Subject: Re: [T10] WRITE SAME and 0 LBA counts
> 
> Looking only at the SBC-4 text fragments quoted by David Black, I can
> find no place where adding the word "computed" will serve any purpose
> other than an increase in confusion.
> 
> That said, however, it would appear that the two quoted SBC-4 text
> citations profoundly violate T10's "say it the same way everywhere"
> strong recommendation (i.e., rule).
> 
> One citation talks about "the number of contiguous logical blocks that
> are requested to be unmapped or written".
> 
> The other citation says "the number of logical blocks specified to be
> unmapped or written".
> 
> David can freely drop the "contiguous" and substitute "specified" for
> "requested", but (when the case is put this plainly) I'll bet steam will
> begin to emanate from George's ears (to name just one of the rule's
> proponents).
> 
> Therefore ...
> 
> Although I cannot support adding "computed" anywhere, I see no reason
> why the SBC-4 editor cannot step in, pick a single phrase to describe
> the quantity, and cause that phrase to be used consistently.
> 
> In the event that the SBC-4 editor decides to solicit guidance from this
> reflector, my vote is for the wording with "contiguous" and "requested"
> in it.
> 
> All the best,
> 
> .Ralph
> 
> On 5/21/2016 12:08 AM, Sitsofe Wheeler wrote:
> >
> >
> > On 19 May 2016 at 02:08, Black, David <david.black at emc.com
> > <mailto:david.black at emc.com>> wrote:
> >
> >     As for the original question:
> >
> >     >When the spec says "number of logical blocks specified to be [...]
> >     written" is this only in reference to the NUMBER OF LOGICAL BLOCKS
> >
> >     > passed in rather than the computed number of blocks to be written or is
> there a choice over which is used
> >     (i.e. the target can pick
> >
> >     > whether it errors or not if the computed blocks exceed the MAXIMUM
> WRITE SAME LENGTH)?
> >
> >     Neither - my reading of the current SBC-4 text is that the limit
> >     always applies to the number of blocks written by the command, but
> >     a careful reading of the text is involved to reach that
> >     conclusion.  Excerpts that follow are from 5.47 WRITE SAME (10) in
> >     SBC-4 rev 10:
> >
> >     If the WSNZ bit is set to zero, then a NUMBER OF LOGICAL BLOCKS
> >     field set to zero specifies that the number of
> >
> >     contiguous logical blocks that are requested to be unmapped or
> >     written includes all of the logical blocks
> >
> >     starting with the LBA specified in the LOGICAL BLOCK ADDRESS field
> >     to the last logical block on the medium.
> >
> >     Note the use of "specifies" in the first line.
> >
> >     If the number of logical blocks specified to be unmapped or
> >     written exceeds the value indicated in the
> >
> >     MAXIMUM WRITE SAME LENGTH field(see 6.6.4), then the device server
> >     shall
> >
> >     terminate the command with CHECK CONDITION status with the sense
> >     key set to ILLEGAL REQUEST and
> >
> >     the additional sense code set to INVALID FIELD IN CDB.
> >
> >     Note the use of "specified" in the first line.
> >
> >     So, a NUMBER OF LOGICAL BLOCKS field set to zero specifies that
> >     all of the logical blocks up to the end of the medium are to be
> >     unmapped or written, and if that (computed) number of logical
> >     blocks exceeds the MAXIMUM WRITE SAME LENGTH value, the required
> >     result is CHECK CONDITION, ILLEGAL REQUEST, INVALID FIELD IN CDB.
> >
> >     >For example, if I have an *SBC-3* 1GByte target with a WSNZ of 0
> >     and a MAXIMUM WRITE SAME LENGTH of 131072 blocks
> >
> >     > (64Mbytes with a sector size of 512), then I issue a WRITE SAME with
> NUMBER OF LOGICAL BLOCKS of 0 and a
> >
> >     > LOGICAL BLOCK ADDRESS of 0 is it legal for the SBC-3 target to produce an
> error because the computed number of
> >
> >     > blocks to be written will be greater than 131072?
> >
> >     That is not only "legal", it is also the behavior required by the
> >     standard.
> >
> >     I believe the standard is unambiguous as written, but I'd support
> >     an editorial clarification to reduce the degree of careful reading
> >     required to reach that conclusion.
> >
> >
> > The minor clarifications (where you added the word "computed" in
> > brackets) were helpful and I'd say it would be helpful in the spec.
> > Whatever happens thanks for clearing up the only acceptable behaviour!
> >
> > --
> > Sitsofe | http://sucs.org/~sits/ <http://sucs.org/%7Esits/>
> >
> >
> > _______________________________________________
> > T10 mailing list
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> > http://www.t10.org/mailman/listinfo/t10
> 
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