On Tue, 28 Nov 2006, Richard Scobie wrote:

Anyway, my biggest concern is why

echo repair > /sys/block/md5/md/sync_action

appeared to have no effect at all, when I understand that it should re-write
unreadable sectors?

i've had the same thing happen on a seagate 7200.8 pata 400GB... and went 
through the same sequence of operations you described, and the dd fixed 
it.

one theory was that i lucked out and the pending sectors in the unused 
disk near the md superblock... but since that's in general only about 90KB 
of disk i was kind of skeptical.  it's certainly possible, but seems 
unlikely.

another theory is that a pending sector doesn't always result in a read 
error -- i.e. depending on temperature?  but the question is, why wouldn't 
the disk try rewriting it if it does get a successful read.

i wish hard drives were a little less voodoo.

-dean