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

In the last episode (Sep 23), Jia-Shiun Li said:
> On Wed, Sep 18, 2013 at 10:49 PM, Ravi Pokala <[email protected]> wrote:
> > 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.

I don't think there are any yet, but some SATA->USB drive enclosures will
present a 4Kn drive to the host if the physical drive is 512e.  The Seagate
Backup Plus does this at least.  It lets you continue to use MBR-based
partitioning and still access all of a 4TB disk.  Unfortunately, since both
GPT and MBR work off of block offsets, partitions created in one mode won't
work in the other, so you can't just swap a disk in and out of the enclosure
without (carefully) repartitioning.
 
-- 
	Dan Nelson
	[email protected]
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