Re: RAIDframe: what if a disc fails during copyback

[oster%netbsd.org@localhost]

On 10/29/20 11:33 AM, Edgar Fuß wrote:
> (I could probably direct this question to oster@ instead of tech-kern@)
>
> In a RAIDframe RAID-1, a disc failed and I reconstructed on a spare.
> Now I want to replace the failed component (actually by the same disc,
> which needed a firmware update) and want to copyback to it.
> How will RAIDframe behave if, during the copyback:
> 1. The replaced component fails

This is a NOP, as it's already failed, and only the non-failed component 
will be considered.

> 2. The spare fails

You're back to considering only the non-failed component.

> 3. The other, non-replaced component fails?

Since the rebuild is done, you can use the rebuilt component to continue on.

> Specifically: Is there any szenario (other than more than one disc failing)
> that will put the RAID into a non-redundant state? I guess 3. may?

2 or 3 will put you back to non-redunant.

However: You really don't want to be using copyback.....  it's still 
there, and it does work, but it's not at all performant or 
system-friendly.  Just put in the new component, reconstruct to it, and 
then call it a day.  If you want the components labelled nicely, give 
the system a reboot (ya, not ideal, but that's where we are).

Basically the copyback code doesn't have the same IO structure as a 
reconstruct, and behaves very poorly.  Copyback should really be just 
ripped out or at least ignored.

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.)

Later...

Greg Oster