[ale] OT: WD "Advanced Format" and "Green Drives"

[Michael Trausch]

On Fri, 2010-04-09 at 13:45 -0400, Greg Freemyer wrote:
> I would avoid drives with 4KiB physical blocks for a while longer
> unless you want to take extra care about alignment etc.

It should not be a great issue; the only thing that you have to be sure
about is to align the start of a partition correctly.  The ext2/3/4
family of filesystems already uses 4KiB blocks by default for many
configurations, and so honestly the only real care that you have to take
is to be sure that the start of the first 4KiB block is on a native
boundary.

I would wager a guess that it would be better if the drives didn't try
to go to the trouble of being "backwards compatible".  If you get a 4KiB
sector drive, I'd see if you can get it to work by not emulating 512
byte sectors, as the partitioning and filesystem utilities are likely to
be able to make more efficient use of the drive's sectors if they know
the true sector size of the drive.  You will need to pull patches from
the libata-dev.git tree's "sectsize" branch (see http://is.gd/bm8wa for
information) as full support for 4 KiB sectors is not yet in the
mainline Linux kernel.  As I understand it, though, that is on the list
for things to make it into 2.6.34.

> As an example parted only got alignment support for them in Dec. 2009
> (parted 2.0 or 2.1)
> 
> My preferred distro is OpenSuse they only got that version of parted
> into their factory distro source code last friday.  It is supposed to
> part of the "milestone 5" release they are doing over the weekend, but
> milestone 5 is effectively a alpha release of the distro.
> 
> So I would have to be using a alpha release of that distro to get true
> 4KiB partition alignment support.
> 
> And at this point no one has even reported testing the full alpha
> release against a 4 KiB drive.
> 
> There first released version with support will be 11.3 that comes out
> in July.

Even without the support, you can use regular fdisk (or write a script
that uses sfdisk) to handle the alignment issues for you on a drive that
emulates 512 byte sectors and only exposes those to the operating
system/SATA firmware.

The one thing that I didn't realize is that the 512-byte sector is
assumed (read: hard-coded) into a lot of software at many levels.  I
cannot find it at the moment, but I could have sworn that there was a
command in the ATA/SCSI command sets that an operating system or disk
driver could use to determine the underlying device's sector size.
While sectors that are not 512 bytes have not been (at least AIUI)
relatively common, they are (again, AIUI) possible and out there.  I
know that CD/DVD/BD media and drives are one example of non-512 byte
sectors, but I thought that there were already magnetic and flash media
that had sector sizes that were different from 512 bytes.

	--- Mike