Re: RAIDframe: what if a disc fails during copyback

[Greg Oster <oster%netbsd.org@localhost>]

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. :(

Later...

Greg Oster