RAID 0+1

[Gordon Messmer]

Jeff Vian wrote:
> Why not raid 5?  The available space is n-1 for the number of drives
> used.

Read and write performance are both significantly better under RAID 10. 
  The only reason to use RAID 5 over RAID 10 is cost.  If you can't 
afford (or justify) RAID 10, then RAID 5 is a lower-cost, 
lower-performance option.

> A single disk problem takes out the entire mirror
> copy (3 disks) because of striping.

If you strip sets of RAID 1 devices, then you'll only have to rebuild 
the disk that fails, when it's replaced.

> A data error on one copy and any
> other error (even in a different location) on the second copy will take
> everything out (again because of the striping effect of raid 0). 

Simultaneous errors on multiple drives will take out pretty much any 
RAID setup.

> The same 6 drives in raid 5 would give you 5*73 or 365gb of space and a
> single drive failure would not in any way harm your data. The redundant
> drive feature would keep everything working while the one drive is
> replaced.

But a data error on one drive, and any other error on another drive will 
prevent you from rebuilding the array, possibly destroying the entire 
thing.  Alarmist, isn't it?

RAID is not a replacement for backups.