[vdr] mdadm software raid5 arrays?

[H. Langos]

On Tue, Nov 10, 2009 at 09:46:52PM +1300, Simon Baxter wrote:
> What about a simple raid 1 mirror set?
>

Ok.. short comparison, using a single disk as baseline.

using 2 disks
raid0: (striping)
 ++   double read throughput, 
 ++   double write throughput, 
 --   half the reliability (read: only use with good backup!)

raid1: (mirroring)
 ++   double read throughput.
 o    same write throughput
 ++   double the reliability


using 3 disks:

raid0: striping
 +++  tripple read performance
 +++  tripple write performance
 ---  third of reliability

raid1: mirroring
 +++  tripple read performance
 o    same write throughput
 +++  tripple reliability

raid5: (distributed parity)
 +++  tripple read performance
 -    lower write performance (not due to the second write but due 
      to the necessary reads)
 +    sustains failure of any one drive in the set

using 4 disks:

raid1+0:
 ++++ four times the read performance 
 ++   double write performance
 ++   double reliability


please note: these are approximations and depending on your hardware
they may be off by quite a bit.

cheers
-henrik