Re: RAID Levels

From: Holger Baer <holger.baer_at_science-computing.de>
Date: Tue, 15 Jul 2003 17:07:14 +0200
Message-ID: <3F1418A2.80002@science-computing.de>

Brian Peasland wrote:
>
> Many people prefer the redundancy of mirroring, coupled with the speed
> of striping so they combine RAID 0 and RAID 1 to get RAID 0+1. This may
> be what you are referring to as RAID 10.
>

There is actually a difference between RAID 1+0 and RAID 0+1. However, this is not immediate obvious.

If you take e.g. 8 Disks, create 4 mirrors spanning 2 disks each and then create a stripe on top on the 4 mirrors (now we have RAID 10), this is quite different to create 2 stripesets across 4 disks each and mirror them (which is RAID 0+1).

Now in case of RAID 10, if two drives fail, they must be the two drives that make up one of the 4 mirrors for the whole raid to bekome unusable.

In case of RAID 0+1, if in both mirrors one disk fails, the complete RAID is unusable.

Let me thank at this point Jonathan Lewis, who explained the concept pretty clear in his brilliant book.

HTH Holger Received on Tue Jul 15 2003 - 10:07:14 CDT