On Wed Dec 19, 2007 at 09:50:16AM -0500, Justin Piszcz wrote:

The (up to) 30% percent figure is mentioned here:
http://insights.oetiker.ch/linux/raidoptimization.html

That looks to be referring to partitioning a RAID device - this'll only
apply to hardware RAID or partitionable software RAID, not to the normal
use case.  When you're creating an array out of standard partitions then
you know the array stripe size will align with the disks (there's no way
it cannot), and you can set the filesystem stripe size to align as well
(XFS will do this automatically).

I've actually done tests on this with hardware RAID to try to find the
correct partition offset, but wasn't able to see any difference (using
bonnie++ and moving the partition start by one sector at a time).

# fdisk -l /dev/sdc

Disk /dev/sdc: 150.0 GB, 150039945216 bytes
255 heads, 63 sectors/track, 18241 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x5667c24a

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1               1       18241   146520801   fd  Linux raid 
autodetect

This looks to be a normal disk - the partition offsets shouldn't be
relevant here (barring any knowledge of the actual physical disk layout
anyway, and block remapping may well make that rather irrelevant).

That's my take on this one anyway.

Cheers,
        Robin
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