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

Ravi Pokala rp_freebsd at mac.com
Mon Sep 23 16:05:21 UTC 2013

-----Original Message-----
From: <rozhuk.im at gmail.com>
Reply-To: <Rozhuk.IM at gmail.com>
Date: Monday, September 23, 2013 1:13 AM
To: 'Jia-Shiun Li' <jiashiun at gmail.com>, Ravi Pokala <rp_freebsd at mac.com>
Cc: <freebsd-hackers at freebsd.org>, <freebsd-hardware at freebsd.org>
Subject: RE: What's the state of AF-4Kn support?

># install
>gpart create -s GPT ada1
>gpart show
>gpart add -i 1 -t freebsd-boot -b 40 -s 512 ada1
>gpart add -i 2 -t freebsd-ufs -b 552 -s ..... ada1
>gpart bootcode -b /boot/pmbr ada1
>gpart bootcode -p /boot/gptboot -i 1 ada1
># for data
>gpart create -s GPT ada1
>gpart show
>gpart add -i 1 -t freebsd-ufs -b 40 -s ..... ada1

Thanks Rozhuk,

As it happens, I know how to create a GPT table and make sure the
partitions are aligned. That's certainly a necessary step for getting good
performance on AF-512e drives, but it doesn't have much to do with booting
from an AF-4Kn drive. (Actually, since GPT is defined in terms of physical
sectors, we can actually *stop* playing silly alignment games with AF-4Kn,
since it is inherently aligned.)


>> -----Original Message-----
>> From: owner-freebsd-hackers at freebsd.org [mailto:owner-freebsd-
>> hackers at freebsd.org] On Behalf Of Jia-Shiun Li
>> Sent: Monday, September 23, 2013 10:23 AM
>> To: Ravi Pokala
>> Cc: freebsd-hackers at freebsd.org; freebsd-hardware at freebsd.org
>> Subject: Re: What's the state of AF-4Kn support?
>> 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.
>> > 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.htm
>> > l ]; 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.
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