On Thu, 28 Aug 2003, Vivek Khera wrote:

> I just ran a handful of tests on a 14-disk array on a SCSI hardware
> RAID card.


> Has anyone else done similar tests of different RAID levels?  What
> were your conclusions?

Yes I have.  I had a 6 disk array plus 2 disks inside my machine (this was 
on a Sparc 20 with 4 narrow SCSI channels and the disks spread across them 
evenly, using RH6.2 and linux sw raid.

My results were about the same as yours, RAID1+0 tended to beat RAID5 at 
reads, while RAID5 tended to win at writes.

There's an old wive's tale that RAID5 has to touch every single disk in a 
stripe when writing, which simply isn't true.  I believe that many old 
controllers (decades back, 286 land kinda stuff) might have done it this 
way, and so people kept thinking this was how RAID5 worked, and avoided 

My experience has been that once you get past 6 disks, RAID5 is faster 
than RAID1+0.

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