I introduced a bug in 15-113

Gerry Houlder gerry.houlder at seagate.com
Fri Jun 5 14:14:23 PDT 2015


Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1506054_f.htm">HTML-formatted message</a>

There are two ways to think about this for sequential write preferred.
(a) Explictly opened zones have a maximum limit because there is a desire
to promise no performance loss for zones that are explicitly opened. This
limit is probably higher than the optimal number of open zones or it might
be the same. If the disk drive has to prevent new explicit opens from
happening, then OPEN ZONE commands are rejected just like they would be on
sequential write required zones.
(b) The other option (which is the thought currently in the standard) is
that sequential write preferred provide no promise of better performance
for particular zones once the optimal number is exceeded. if the host
insists on opening more zones (either implictly or explicitly) without
actions to close or fill some zones, then the disk drive allocates
performance resources to whatever zone(s) seem to be most active in a
vendor specific manner (regardless of their implicit or explict attribute).
Behavior (a) introduces a "more likely to want better performance" hint
that is absent from the ZBC standard. However, sequential write preferred
is already documented to accept and process everything the host sends and
if the host willfully ignores the drive's reported optimal limits then some
commands will have lower performance than would usually be expected and the
drive becomes the arbiter of how to maintain best performance. Going above
the optimal limit should cause the drive to react as if all open zones are
implicitly open, but none will be implicitly closed.
On Fri, Jun 5, 2015 at 3:07 PM, Joe Breher <Joe.Breher at hgst.com> wrote:
>  Hi Ralph -
>
>  I hate to be disagreeable, but I disagree with your disagreement.
>
>  The page 9 comment I wish to retract is not in 4.3.3.op.6.3, but in
*4.3.3.op.6.2
>  Select a sequential write preferred zone*, where I commented "All zone
> management operations to sequential write preferred zones return successful
> completion."
>
>  There is a very real limit on the number of concurrent explicitly open
> sequential write preferred zones a device is able to support - for at least
> some implementations. If this limit is reached, and there are no implicitly
> open sequential write preferred zones, the device must fail the zone
> management operation, as the guiding directive is that zone management
> operations shall not cause explicitly open zones to be closed. Note the (y
> > 0) term in the expression.
>
>  I realize (now) that we currently have no mechanism to report such a
> limit. This may be the root issue with this feature. We are still
> confabbing internally with the proper resolution of this -- which is why I
> have not yet forwarded proposed text -- but at least one solution is
> immediately apparent. Unfortunately, it introduces a new technical
> requirement at a late date. This would be to introduce a new VPD parameter
> of MAXIMUM NUMBER OF EXPLICITLY OPEN SEQUENTIAL WRITE PREFERRED ZONES, and
> have a secondary test in the 'Select a sequential write preferred zone'
> path.
>
>  Suggestions for a less intrusive resolution are welcome.
>
>     Joe Breher
>  Storage Architecture Technologist
>  Standards Setting Organization
>  San Jose Research Center
>  HGST, a Western Digital company
>  (478) 2-Breher
>  (478) 227-3437
>
>  *This e-mail may contain confidential or legally privileged information
> of HGST. If you are not the intended recipient, please notify us
> immediately by responding to this e-mail and then deleting it from your
> system.*
>
>
>
>
>
>
>
>  On Jun 4, 2015, at 6:59 PM, Ralph Weber <Ralph.Weber at wdc.com> wrote:
>
>  Joe,
>
> I disagree with your retraction of the page 9 comment.
>
> The only way an error is returned is if the second equation in 4.3.3.op.6.3
>  *Select a sequential write required zone* evaluates to true. If the
> values in the equation are spelled out, the following must evaluate to
true:
>
> the number of *sequential write required zones* with a Zone Condition of
> EXPLICITLY OPENED
> ge
> the contents of the MAXIMUM NUMBER OF OPEN SEQUENTIAL WRITE REQUIRED ZONES
> field of the Zoned Block Device Characteristics VPD page
>
> Now, if there is so much as one sequential write preferred zone open,
> then the zoned device is not allowed to support *any* sequential write
> required zones. Therefore, the number of sequential write required zoned
> with a Zone Condition of EXPLICITLY OPENED must be zero.
>
> Surely, zero should be a small enough number to be less than any valid
> contents of the MAXIMUM NUMBER OF OPEN SEQUENTIAL WRITE REQUIRED ZONES
> field, *n'es pas*?
>
> All the best,
>
> .Ralph
>  ------------------------------
> *From:* Joe Breher [Joe.Breher at hgst.com]
> *Sent:* Wednesday, June 03, 2015 10:45 AM
> *To:* Ralph Weber; T10 org
> *Cc:* Gerry Houlder
> *Subject:* ZBC: I introduced a bug in 15-113
>
>   I just realized that I introduced a bug in 15-113r4 as modified.
>
>  On page 9, I commented "All zone management operations to sequential
> write preferred zones return successful completion".However, in the case
> where there are no implicitly opened zones available to be closed (i.e.,
> all open zones are explicitly opened zones), the zone management operation
> will indeed return a non-successful completion.
>
>  I will have suggested text to correct this later today.
>
>     Joe Breher
> Storage Architecture Technologist
> Standards Setting Organization
> San Jose Research Center
> HGST, a Western Digital company
> (478) 2-Breher
> (478) 227-3437
>
> *This e-mail may contain confidential or legally privileged information of
> HGST. If you are not the intended recipient, please notify us immediately
> by responding to this e-mail and then deleting it from your system.*
>
>
>



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