Re: RAID1, changed disk, 2nd has errors ...

Am 2011-08-26 16:08, schrieb Robin Hill:

sda4 is still in the array, with some unreadable sectors. sdb4 is a
 spare because the resync failed due to unreadable sectors on
sda4. You cannot add a disk to an array unless the data can all be
read (or recovered if there's still enough redundancy).

Ah, now I got it.
I misinterpreted this:

md2 : active raid1 sdb4[2](S) sda4[0]
      962454080 blocks [2/1] [U_]

I thought [U_] maps to the first line "sdb4 sda4" and somehow read
"sdb4 is UP and sda4 is down"

I could have seen it at

    Number   Major   Minor   RaidDevice State
       0       8        4        0      active sync   /dev/sda4
       1       0        0        1      removed

       2       8       20        -      spare   /dev/sdb4

but you know, panic ;-)

So basically I am where I was before swapping sdb: everything running
on sda, which has some corrupt sectors. Which may never have been
touched so far.

quoted

As far as I understand it might be possible to spot the defective
 sectors and the related LV?

A read of the relevant block device (dd if=/dev/xxx of=/dev/null) 
will result in read errors for whichever block device contains the 
bad sectors. You could also probably map the sectors reported by
the kernel to the position on the disk to tell what LV it.

There is only 350GB out of ~920GB mapped to active LVs. It might be
the case that the corrupt stuff isn't even mapped yet.

I once knew how to figure that out, I will have a closer look.

quoted

I have backups, yes ...

In which case the absolute safest option is just to recreate 
whatever arrays, PVs, LVs, etc. on sdb4 and restore the data, 
ignoring whatever's on sda4 currently.

I understand now, yes.

quoted

re-adding sda4 and starting such a check would be possible? Or 
would a re-add damage things?

You can't add sda4 because it's already in the array.

Sure, now that I figured out the mentioned misunderstanding.

quoted

Should I shutdown the box for safety?

For absolute safety, yes, though I don't think the risk is too
high at the moment, and I don't think things'll get any worse in
the short term.

That sounds good for my weekend! Thanks ...

quoted

I am really feeling unsafe now, and getting another hdd for 
swapping will take me at least until monday.

(I would like to dd-rescue to another new disk to keep sdb, just
in case)

I doubt you'd be able to recover anything useful from sdb4 at the 
moment, but that's up to you.

Yep, also clear now.
I wait with that ddrescue-stuff anyway.

Thanks for your help!
Stefan