On 9/17/06, Dexter Filmore [off-list ref] wrote:

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It's recommended to use a script to scrub the raid device regularly,
to detect sleeping bad blocks early.

What's the best way to do that?  dd the full md device to /dev/null?

echo check >/sys/block/md?/md/sync_action

Distros may have cron scripts to do this "right".

And you need a fairly recent kernel.

Does this test stress the discs a lot, like a resync?
How long does it take?
Can I use it on a mounted array?

yup.
long. think resync.
yup.

It's practically "read everything, verify checksum, report bad blocks
or inconsistencies".

echo repair>sync_action causes md to fix redundancy blocks if they're
out of sync (but at that point you already have another problem like
flakey hardware or so)