[T10] WRITE SAME and 0 LBA counts

Ralph Weber roweber at ieee.org
Mon May 23 07:53:55 PDT 2016


Gerry,

I was all set to agree with this sentiment until the following 
definition was found in the WRITE (10) command subclause.

 >> The TRANSFER LENGTH field specifies the number of contiguous logical 
blocks of data that shall be transferred ...

Consistency of wording throughout SBC-4 dictates the use of "contiguous" 
in this case too.

All the best,

.Ralph

On 5/23/2016 9:37 AM, Gerry Houlder wrote:
> Since the WRITE SAME command is only able to write one extent of LBAs, 
> all of which are contiguous due to the definition of how the number of 
> blocks field is used, I see no need to have the word contiguous in the 
> description. I am OK with using either specified or requested when 
> referring to the value that is present in the Number of Logical Blocks 
> field.
>
> On Mon, May 23, 2016 at 8:28 AM, George Penokie 
> <george.penokie at broadcom.com <mailto:george.penokie at broadcom.com>> wrote:
>
>     One persons "editorial" change could be another persons
>     "substantive" change. That said the fact that this thread is as
>     long as it is means to be that any change in this area will
>     require a proposal.
>
>     Bye for now,
>     George Penokie
>
>     Broadcom Limited
>     Attn: George Penokie
>     4109 Manor View Dr NW
>     Rochester , MN 55901
>
>     952-921-2495 <tel:952-921-2495>
>     george.penokie at broadcom.com <mailto:george.penokie at avagotech.com>
>
>     On Sun, May 22, 2016 at 5:30 PM, Black, David <david.black at emc.com
>     <mailto:david.black at emc.com>> wrote:
>
>         > 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>
>         [mailto: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 <mailto: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>
>         > > <mailto: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/
>         <https://urldefense.proofpoint.com/v2/url?u=http-3A__sucs.org_-7Esits_&d=CwMFaQ&c=IGDlg0lD0b-nebmJJ0Kp8A&r=TxI1DC4HavpWBdSmUqvdNvSwgOklhaW328zLt5AOpPM&m=wcIDMurF4N3OhN5MOcDA2PPGxRIYlRrsMXuD-usha7Q&s=89fURF_0EDzAobIn6fHYd1DLN_1T2GBXcNdBXQ-AOvI&e=>
>         <http://sucs.org/%7Esits/
>         <https://urldefense.proofpoint.com/v2/url?u=http-3A__sucs.org_-257Esits_&d=CwMFaQ&c=IGDlg0lD0b-nebmJJ0Kp8A&r=TxI1DC4HavpWBdSmUqvdNvSwgOklhaW328zLt5AOpPM&m=wcIDMurF4N3OhN5MOcDA2PPGxRIYlRrsMXuD-usha7Q&s=QZwIO0mZ_ww8qRTUucjPK5MndCPcqKa_iUZ1sJSM7YA&e=>>
>         > >
>         > >
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