linux-kernel - Re: tools support for non-512 byte sector sizes

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Date:	Wed, 30 Jul 2008 19:16:49 +0200
From:	Jim Meyering <jim@...ering.net>
To:	Matt Domsch <Matt_Domsch@...l.com>
Cc:	"Martin K. Petersen" <martin.petersen@...cle.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Matthew Wilcox <matthew@....cx>,
	Ric Wheeler <rwheeler@...hat.com>, linux-scsi@...r.kernel.org,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jeff Garzik <jeff@...zik.org>
Subject: Re: tools support for non-512 byte sector sizes

Matt Domsch <Matt_Domsch@...l.com> wrote:
> On Tue, Jul 29, 2008 at 02:48:31PM -0400, Martin K. Petersen wrote:
...
>> Just yesterday I received a couple of prototype drives in the mail.
>> I'll ask the vendor whether they support 4KB and if so I'll give them
>> a whirl.
>
> I have access to disks with native 4KB sectors now too.  Would

Do they expose that sector size?
I.e., does ioctl(fd,BLKSSZGET,&ss) set ss to 4096?

I'm interested because I'm preparing GNU Parted's partition table
manipulation code (not its FS code) for just that.
In particular, now I've heard two stories:

  - disk makers will eventually sell drives with >512-byte sectors

  - some disk makers have sort of agreed not to do that, and
      expect forever to hide the larger underlying sector size
      behind a virtual 512 (of course, this imposes alignment
      restrictions, but that's a smaller problem)

Even if the latter is the case, we still have to deal with
optical and flash, both of which can already have larger sectors.

> interested parties be willing to share test plans, so we could be sure
> we have coverage wrt correctness: kernel internals, userspace tools like parted,
> fdisk, kpartx, apps using O_DIRECT)?  Benchmarking winds up being an
> NDA activity this early in the game so I don't want the focus of any
> joint work to be benchmarks yet.

Speaking of O_DIRECT, both dd and shred (both in coreutils), use
O_DIRECT, so you could get _some_ coverage just by running shred
and experimenting with dd's oflag=direct and iflag=direct options.
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