Re: ATA 4 KiB sector issues.

[Denys Vlasenko <vda.linux@googlemail.com>]

On Monday 15 March 2010 06:20, david@lang.hm wrote:
> >>> For any other partition, pick start cylinder which is a multiple of 8:
> >>>
> >>> cyl 8*x head 0 sector 1: LBA sector 8*x*255*63 - good (4k aligned)
> >>>
> >>> This will actually work well for *any* geometry, not only for 63s/255h.
> >>
> >> Yes, but it does squat for a flash disk that wants, say, 256K alignment.
> >
> > 4K makes sense. 256K not so much.
> >
> > 256K alignment is hard to swallow for a lot of reasons anyway.
> > Unless the filesystem packs small files into blocks a-la reiserfs,
> > 256K block filesystems will be very inefficient for a typical
> > storage scenarios.
> 
> the thing is, if the OS can learn that it's more efficiant to write in 
> 256K aligned chunks, then it can batch up things so that the drive doesn't 
> have to do a read-modify-write cycle and can instead just replace the 
> entire chunk.

I think Linux already is doing this. The problem is, in many cases
OS can't possibly do this, short of using a specially designed
filesystem.

If you untar a Linux kernel source tarball on a seriously
fragmented ext2 filesystem, there will be a lot of discontiguous
and/or misaligned writes smaller than 256K.
Only smart firmware can help in this case.
-- 
vda