8.04 md raid5 troubleshooting

[compdoc]

>In the meantime the extended selftest finished without problems (the
>only significant difference between the defective drive and the others
>is a reallocated sector count of 1).


Reallocated sectors are why drives drop out of arrays. I've had that problem
with the consumer desktop drives I use in my arrays. I think enterprise
class drives have a feature that overcomes that problem.

Once a drive starts to develop bad sectors it can't be trusted in an array
because if it drops out again, and then another drive drops out for any
reason, you've lost the array. At least that's true with simple arrays up to
and including raid 5.

Replace the drive with a new one - don't use refurbished drives. Once you
have a set of trusted/proven drives, the array can run for years.