What's the state of AF-4Kn support?

[Jia-Shiun Li]

On Wed, Sep 18, 2013 at 10:49 PM, Ravi Pokala <rp_freebsd at mac.com> wrote:
>
> What you describe is the 'AF-512e' format - 4KB physical sectors
> *emulating* 512B logical sectors. See [
> https://en.wikipedia.org/wiki/Advanced_Format#Advanced_Format_512e ;
> http://www.idema.org/?page_id=2153 ]. With AF-512e, yes, the HDD firmware
> does the read/modify/write for I/Os smaller than the physical sector size.
> It is intended to be a low-cost/transitional format, allowing the HDD
> vendors to get the advantages of 4KB physical sectors (better error
> detection/correction algorithms, better areal density => lower cost) w/o
> breaking compatibility with decades of firmware and software that expect
> 512B logical sectors.
>
> What I'm asking about is AF-4kn - 4KB *logical* as well as physical
> sectors. All the enterprise HDD vendors have told us is that AF-4Kn drives
> expect data IO to be 4KB, and will reject smaller transfers. (*metadata*
> IO - SMART, IDENTIFY_DEVICE, READ_LOG/WRITE_LOG, etc - will remain 512B.)
>
> Doing some more digging, I found this post from ivoras which I missed the
> first time around [
> http://ivoras.net/blog/tree/2011-01-01.freebsd-on-4k-sector-drives.html ];
> that tends to support my initial assessment - filesystem stuff should Just
> Work[tm] - plus adds the detail that direct drive I/O (the example he
> gives is trying to `dd' 10 bytes) will be rejected because it is smaller
> than the raw-device access granularity. I've also looked at 'ata_da.c' and
> see that adaregister() looks at both quirks and IDENTIFY_DEVICE data to
> determine the logical block size.
>
> So, that leaves the bootstrap code as the remaining question-mark. Does
> anyone what AF-4Kn support looks like there?
>

CC -hackers.

Thanks for the clarification. Is there any 4Kn HDDs shopping now? I am
not aware of any.

BTW I believe UFS and ZFS have proper design for 4K-sectors, but
FreeBSD needs some ecosystem connections to get samples early to test,
incorporate supports and validate for it. Or we will need to wait
until it appears on market and someone got caught into some kind of
bugs.

Regards,
Jia-Shiun.