Re: opinion on RAID choice

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.

SNIP

> 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
it.

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