Paranoia about DegradedArray

[Hendrik Boom <hendrik@topoi.pooq.com>]

I got the message (via email)

This is an automatically generated mail message from mdadm
running on april

A DegradedArray event had been detected on md device /dev/md0.

Faithfully yours, etc.

P.S. The /proc/mdstat file currently contains the following:

Personalities : [raid1] 
md0 : active raid1 hda3[0]
      242219968 blocks [2/1] [U_]
      
unused devices: <none>


Now I gather from what I've googled that somehow I've got to get the RAID 
to reestablish the failed drive by copying from the nonfailed drive.
I do believe the hardware is basically OK, and that what I've got is 
probably a problem due to a power failure  (We've had a lot of these 
recently) or something transient.

(a) How do I do this?

(b) is hda3 the failed drive, or is it the one that's still working?

-- hendrik