Re: Multi-layer raid status

[Wols Lists <antlists@youngman.org.uk>]

On 02/02/18 10:41, David Brown wrote:
> Using bad block lists and then doing a higher level scrub should
> certainly work, and is a good general solution as it means you don't
> need direct interaction between the layers (just the normal top-down
> processing of layered block devices).  The disadvantage is that there
> may be quite a delay between the raid1 rebuild and the next full re-read
> of the entire raid5 array - all you really need is a single read at the
> higher level to trigger the fixup.

This would be a perfect use case of my "full parity reads" mode ... at
the moment, raid just reads sufficient disks to return the requested
data, but I proposed a mode where it read the full stripe, did the
parity checks, and either returned a read error (2-disk raid-1, raid-5)
or corrected the stripe (raid-6) if things didn't add up.

Okay, it would knacker performance a bit, but where you've got a nested
raid like this, you switch it on, run a read on the filesystem ( tar /
--no-follow > /dev/null sort of thing), and it would sort out integrity
all the way down the stack.

Cheers,
Wol