[parted-devel] 4K sector and alignment support?

[Jeff Garzik]

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