Am 03.05.2011 19:54, schrieb Evgeny Bushkov:
> Hi.
> How can I find out which is the parity disk in a RAID-4 soft array? I
> couldn't find that in the mdadm manual.  I know that RAID-4 features a
> dedicated parity disk that is usually the bottleneck of the array, so
> that disk must be as fast as possible. It seems useful to employ a few
> slow disks with a relatively fast disk in such a RAID-4 array.
> 
> Best regards,
> Bushkov E.
> 

You are seriously considering a RAID4? You know, there is a reason why
it was superseded by RAID5. Given the way RAID4 operates, a first guess
for finding the parity disk in a running array would be the one with the
worst SMART data. It is the parity disk that dies the soonest.

From looking at the source code it seems like the last specified disk is
parity. Disclaimer: I'm no kernel hacker and I have only inspected the
code, not tried to understand the whole MD subsystem.

Regards,
Florian Philipp