From owner-freebsd-fs@FreeBSD.ORG  Wed Oct 12 17:43:24 2011
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Date: Wed, 12 Oct 2011 10:43:23 -0700
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From: Artem Belevich <art@freebsd.org>
To: Jeremy Chadwick <freebsd@jdc.parodius.com>
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Subject: Re: AF (4096 byte sector) drives: Can you mix/match in a ZFS pool?
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On Wed, Oct 12, 2011 at 10:29 AM, Jeremy Chadwick
<freebsd@jdc.parodius.com> wrote:
> How does ZFS determine this? =A0I was under the impression that this
> behaviour was determined by (or "assisted by") ashift.
>
> Surely ZFS cannot ask the underlying storage provider (e.g. GEOM on
> FreeBSD) what logical vs. physical sector size to use (e.g. for SATA
> what's returned in the ATA IDENTIFY payload), because on SSDs such as
> Intel SSDs *both* of those sizes are reported as 512 bytes (camcontrol
> identify confirms).

In r222520 mav@ added ADA_Q_4K quirks for bunch of Hitachi, Seagate
and WD drives so that geom_disk will be aware of 4K sectors at least
for some disks.
I'm not sure whether ZFS picks it up, though.

--Artem