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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