Re: RAID 5 vs RAID 10 benchmark

Jonathan Lewis wrote:
> Sorry about the delay in replying. Two weeks
> out of the country, and lots to catch up on.
>
> I rarely get the numbers right, but a fixed parity
> disk is either RAID-3 or RAID-4. When you
> move to RAID-5, I believe the parity is described
> as 'block-level rotating parity', so every disc gets
> a fair share.
>
> A pattern across five disc would look something
> like the following (where D = data and P = parity
> block).
>
> D D D D P
> D D D P D
> D D P D D
> D P D D D
> P D D D D
>

RAID-3 as well as 4 have a fixed parity disk. You are correct about RAID-5.

In addition to the redundancy in data, the Hamming codes used for parity calculations, can recreate the missing parity bit from remaining disks, thus allowing one disk to go bad.
However, 2 bits cannot be recalculated
(aka when 2 disks go bad: failure).

For other definitions, benefits and drawbacks, these are nice:
http://www.uni-mainz.de/~neuffer/scsi/what_is_raid.html http://www.acnc.com/04_01_03.html
Last link has RAID10, too, the first has not

-- 
Regards,
Frank van Bortel