zbc theory of operation

Gerry Houlder gerry.houlder at seagate.com
Tue Aug 5 08:05:33 PDT 2014


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You have made a reasonable request. i will make sure this idea is discussed
at the next ZBC meeting Aug. 21.
This has not been considered a big issue because we think that a
"reasonable implementation" with use zones that have the same number of
LBAs in each zone. In this case an initiator only need to know the zone
size to easily calculate the correct starting address of each zone. The
SAME bit was added to the header of the REPORT ZONES parameter data to
indicate that a host can depend on this characteristic. The standard is
written to accommodate products that will have a large conventional zone
plus a number of smaller write pointer zones because this is envisioned as
having a market demand as well as products that have zones that are all the
same size. I personally think that systems don't want to have to keep a
possibly different zone map for each drive.
I also envision that systems will want all of the zoned block devices in
the system to have the same zone size. This would greatly simplify the
system's task to find the start of a zone in any particular drive in the
system.
On Tue, Aug 5, 2014 at 7:51 AM, Hannes Reinecke <hare at suse.de> wrote:
> * From the T10 Reflector (t10 at t10.org), posted by:
> * Hannes Reinecke <hare at suse.de>
> *
> Hi all,
>
> I know ZBC is still far from being final, but nevertheless I've got some
> questions / issues which I've stumbled across recently.
>
> The most crucial one is how to get the zone information for any given LBA.
> Typically one would use the REPORT ZONES command to retrieve the zone
> information for a given LBA.
>
> However, zbc01 states that the REPORT ZONES will fail if the LBA is _not_
> the starting LBA of a zone.
>
> Which means we have to have an a-priory knowledge of the zone layout, ie
> we have to trawl through _all_ zone information before we can use REPORT
> ZONES with a non-zero LBA.
> But if we have to slurp in _all_ zones before we can use the REPORT ZONES
> command in a meaningful manner it makes me wonder how it is supposed to be
> used.
> Plus slurping in all zones upon startup takes up quite some time; I've
> measured several _minutes_ to retrieve the full zone information.
>
> So how is the REPORT ZONES command to be used without a-priory knowledge
> of the zone layout?
>
> Life would be _so much_ easier if we could lift the restriction on the
> REPORT ZONES command, so that it'll always return the zone information the
> LBA is contained in.
>
> Cheers,
>
> Hannes
> --
> Dr. Hannes Reinecke			zSeries & Storage
> hare at suse.de				+49 911 74053 688
> SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
> GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
> *
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