Neil Brown wrote:

If the array is marked read-only, it wont do a scrub.

However if you simply don't have any filesystem mounted, then the array
will remain 'clean' and any failures are less likely cause further
failures.

So doing it off line is a good idea, but setting the array to read-only
won't work.
  

Thanks for the info Neil,
would mounting the filesystems readonly be safe in the same way?
(I might try to rsync some data out during the scrub)
Thank you
Asdo