[CentOS] Raid 10 questions...2 drive

Benjamin Franz jfranz at freerun.com
Sat Sep 25 08:06:43 EDT 2010


On 09/24/2010 07:50 PM, Digimer wrote:
> Raid 10 requires 4 drives. First you would make two RAID 0 arrays, then
> create a third array that is RAID 1 using the two RAID 0 arrays for it's
> devices.
>
> With only two drives, your option is RAID 1 (mirroring - proper
> redundancy) or RAID 0 (striping only - lose one drive and you lose *all*
> data).
>
>    

That's 0+1 not 1+0.

And don't do it that way.

If you have a single drive failure with RAID 0+1 you've lost *all* of 
your redundancy - one more failure and you are dead. If you create two 
RAID1 sets and then strip them into a RAID0 you get pretty much the same 
performance and space efficiency characteristics, but if you have a 
drive failure you still have partial redundancy. You could actually take 
a *second* drive failure as long as it was in the other RAID1 pair. With 
4 drives raid0+1 can only survive 1 drive failure. With 4 drives in raid 
1+0 you can survive an average of 1.67 drive failures.

-- 
Benjamin Franz


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