Re: testing raid 0

["Anil Madhavapeddy" <anil@recoil.org>]

Aaron Crandall wrote:
>
> RAID 4 (yes, Network Appliance filers use it) is very
> specialized and even faster than RAID 5.

Sort of - RAID4 isn't faster in the general case.  It uses a single
parity disk, so if you are doing a lot of writes, then the one disk
quickly becomes a bottleneck.

NetApp Filers use it because they have a large wad of NVRAM in which
writes are logged and buffered, and then written to disk in one pass
after a certain amount accumulates - this way, they can implement RAID
without any performance hit over normal storage (in fact, a lot faster
due to the way the WAFL filesystem works).

Obviously, you need a lot of NVRAM for this journalling buffer,
otherwise you sacrifice reliability in the case of power failure.

Anil