On Mon, 2010-01-11 at 15:05 +0100, Pavel Machek wrote:
> On Fri 2010-01-08 13:43:47, H. Peter Anvin wrote:
> > On 01/08/2010 01:33 AM, Karel Zak wrote:
> > >
> > > fdisk:
> > > - the fdisk command aligns newly created partitions to minimum_io_size
> > > boundary ("minimum_io_size" is physical sector size or stripe chunk
> > > size on RAIDs).
> > >
> > > - the fdisk command supports disks with alignment_offset now.
> > >
> >
> > I think we should align, by default, much more aggressively than that --
> > because frequently we just don't know what the real physical alignment
> > is (think of flash media, which uses large erase blocks underneath.)
>
> Flash has special mapping layer, and does not care (SD/MMC), or is a
> raw nand and can't be used as block device (smartmedia).
MMC does care, and we measured it, non-4KiB aligned writes were
noticeably slower on real eMMC and some MMC cards. I cannot remember the
numbers, but I vaguely recall something like 11%.
So the first statement is incorrect. It really does matter. E.g., we
observed that FAT FS was slower if the partition did not start from 4KiB
boundary.
--
Best Regards,
Artem Bityutskiy (Артём Битюцкий)
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