[wellylug] Raid 0 multidisc

Jethro Carr jethro.carr at jethrocarr.com
Sun Apr 6 01:31:01 NZDT 2008


On Mon, 2008-03-31 at 11:57 +1300, E Chalaron wrote:
> Hi There
> A quick question about Raid 0, if you have 2 disks of same size in Raid 
> 0, you would probably get the expected perf.
> 
> Now if you had a third disk with same filesystemand same size ? What 
> sort of extra perf can you expect ?
> 
> And if the 3rd disk is a little bit smaller in capacity

Well, that will depend a lot on how you have your RAID configured and
the type of data you are processing.

If your files are larger than the stripe size, all 3 drives will have to
seek to get the file, reducing your seek time to the speed of a single
drive.

Data transfer rate will depend on the maximum speed of your RAID
controller, but in theory will increase with the number of drives that
you have.

Wikipedia has a few notes explaining the seek stuff:
http://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_0_performance

So, questions to help get a better answer:
* What sort of disk controller are you using?
* Are you using hardware or software raid? And if hardware, what is the
chipset?
* What is your stripe size?
* What is the typical size of files that will be stored on the drives?


Understand that disk performance will depend on a lot of factors, so
it's not really possible to give you a good answer here.


-- 
Jethro Carr

www.jethrocarr.com
www.jethrocarr.com/index.php?cms=blog

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