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SubjectRe: ATA 4 KiB sector issues.
>>>>> "James" == James Bottomley <> writes:

James> However, for 4k sectors, the main issues which have shown up in
James> testing by others (mostly Martin) are

James> 1. In native 4k mode, we work perfectly fine. *however*,
James> most BIOSs can't boot native 4k drives.

Correct. I have engaged with pretty much all the big OEMs in the
industry and so far the interest has been near zero.

James> 4. The aligment problem is made more complex by drives that
James> make use of the offset exponent feature (what you refer
James> to as offset by one) ... fortunately very few of these
James> have been seen in the wild and we're hopeful they can be
James> shot before they breed.

This topic is constantly up for debate in IDEMA. However, it looks like
we might win because of the impending demise of XP.

James> so the bottom line seems to be that if you want the device as a
James> non boot disk, use native 4k sectors and a non-msdos partition
James> label. If you want to boot from the drive and your bios won't
James> book 4k natively, partition everything using the 512 emulation
James> and try to align the partitions correctly. If your bios/uefi
James> will boot 4k natively, just use it and whatever partition label
James> the bios/uefi supports.

James> Martin can fill in the pieces I've left out.

Here's my latest take given what I hear on the grapevine:

1. 512-byte logical block size drives will be around forever for legacy
deployments because nobody is willing to do the required BIOS int13
work. It's not just a BIOS thing, this requires heavy changes to HBA
boot ROMs as well.

2. Some vendors are working on EFI firmware and will support booting off
of 4KB LBS drives there. This is mostly aimed at the server space.

3. 4 KB logical block size drives will mainly be targeted for use inside
arrays. Off the shelf enterprise drive models will most likely
continue to ship with a 512-byte LBS.

4. Part of the hesitation to work on booting off of 4 KB lbs drives is
motivated by a general trend in the industry to move boot
functionality to SSD. There are 4 KB LBS SSDs out there but in
general the industry is sticking to ATA for local boot.

Martin K. Petersen Oracle Linux Engineering

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