[parted-devel] 4K sector and alignment support?
Jeff Garzik
jeff at garzik.org
Fri Dec 7 22:16:47 UTC 2007
Jim Meyering wrote:
> Maybe all parted needs is a way to determine what alignment is required
> on these new disks.
If you have the necessary alignment stuff already, then indeed, all you
need is a way to obtain the ATA "IDENTIFY DEVICE" information from the
device, something reasonably straightforward for most parted users like
OS installers.
> When are they expected to hit the market?
Under 12 months. I have samples now, but dunno when they will be in the
field.
FWIW the drive industry is _really_ trying to play this one safe, and
IMO I actually think they are playing it /too/ safe given the minimal
adverse impact I think it will ultimately have. But hey, better too
careful than not careful enough.
> BTW, I spent some time making parted work with sector sizes > 512 a few
> months ago. Simulating larger sector sizes invariably provoked stack
> overruns and other nastiness. It's a pretty big mess. I fixed a few,
> and have some unfinished patches: other projects took priority. Does
> anyone care about larger-than-512-byte sector sizes?
Definitely; That's coming down the pipe too.
The drive industry is first going to a 1K/512b or 4K/512b configuration.
That is, a 1K phyical sector under the hood, but presented via the
familiar 512-byte logical sector interface. 4K/512b == 4K physical
sectors on the platter, 512-byte logical interface to the OS.
At this stage, the OS merely needs to make sure data is sufficiently
aligned so as to not punish the host with read-modify-write cycles.
The next step is 1K/1K or 4K/4K, where the ATA command interface is
changed -- for the first time ever -- to use sectors larger than 512 bytes.
At this stage, alignment issues disappear again, but we break all the
512-byte assumptions hardcoded for decades into software. The Linux
kernel is lucky: we had to deal with 1K hardware sector sizes long ago,
for situations such as WORM devices.
Now the long task of evaluating all the non-kernel software begins :)
Regards,
Jeff
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