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Re: RAIDframe: what if a disc fails during copyback

On 10/30/20 4:25 AM, Edgar Fuß wrote:
Thanks for the detailed answer.

it's still there, and it does work,
That's reassuring to know.

but it's not at all performant or system-friendly.
Just how bad is it?

It's been probably over a decade since I last tried it, but as I recall it locks out all other non-copyback IO in order to finish the job!

If you want the components labelled nicely, give the system a reboot
Re-booting our file server is something I like to avoid.

You'll like copyback even less then -- I'd say once you're done reconstruct, just leave it, or reconstruct again to the 'repaired original' as I suggested...

and behaves very poorly.
Depending on how poorly, I could probably live with it (the RAID in question
is the small system one, not the large user data one).

Locking out all other IO is very poor... but if it's a small enough RAID set you might be able to get away with the downtime for the copyback...

In your case, what I'd do is just fail the spare, and initiate a reconstruct
to the original failed component.  (You still have the data on the spare if
something goes back with the original good component.)
Hm, I guess I would need to re-boot and intervene manually in that case.
Just using the slow copyback looks preferrable if it doesn't take more than
a day.

You shouldn't need to reboot for this... the 'failing spared disk' and 'reconstruct to previous second disk' should work fine without reboot. (IIRC I've used a '3rd component' to make the primary/secondary components swap places.. just to test that, of course :) )

Probably I need to test this on another machine before.
I guess there's no way to initiate a reconstruction to a spare and failing
the specified component only /after/ the reconstruction has completed,
not before?

No, there's not, unfortunately. :(


Greg Oster

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