[ale] RAID5 chunksize?

[Danny Cox]

Robert,

On Tue, 2002-12-10 at 10:29, Robert L. Harris wrote:
> What is the ideal Chunksize?  

	Well, you'll have to test.  In my case, with 85GB IDE IBM DeathStar,
um, that is DeskStar drives, in a 4 drive RAID-5, I found the larger the
better.  I tried every block size from 4K through 2M, and each step up
got a little faster.  However, the larger you went, difference became
smaller.

	I was also using XFS, and I tested using bonnie.  So, that's just one
data point.  If you have the time, make a small partition (otherwise the
RAID rebuild will take a LONG time) near the middle of the disk (to get
the average speed of the disk), and write a script to:

	1) build a RAID-5 with the next chunksize
	2) wait for it to complete (watch /proc/mdstat)
	3) make the fs of your choice
	4) mount it
	5) run some tests
	6) umount it
	7) goto 1 (are gotos legal in text ;-)?
	8) plot the results (use a log scale for the sizes)

-- 
kernel, n.: A part of an operating system that preserves the
medieval traditions of sorcery and black art.

Danny

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