[CentOS] quick question on RAID 1

Sat Aug 13 17:11:13 UTC 2005
Chris Mauritz <chrism at imntv.com>

Ulrik S. Kofod wrote:

>I have 3 disks that I want to setup in a raid 1, my questions is should I setup the
>3rd disk as a spare-disk or should I mirror all 3 disks all the time?
>Will it perform *much* better to only mirror two and have the 3rd as a spare.
>Is it not safer to mirror all 3 drives all the time ?

I really don't understand the question.  RAID-1 requires an even number 
of disks since disk(s) A simply is a mirror image of disk(s) B.  So with 
3 disks you could have a 2-drive mirror and designate the 3rd drive as a 
hot spare.  So if one of your mirrored drives fails, the hot spare takes 
over.  You could just as easily do a 3-disk RAID-5 array.  It would be 
substantially faster on reads than a 2-disk mirror.  It could be faster 
or slower on writes depending on which hardware RAID card you're using 
or how fast your processor is if you're doing software RAID.