Re: RAID-6 mdadm disks out of sync issue (five questions)

[<linux-raid.vger.kernel.org@atu.cjb.net>]

NeilBrown <neilb@suse.de> wrote :
> Once you are sure you have the 6 drives with the highest
> event counts working, assemble them with
>
> mdadm --assemble /dev/md13 --force /dev/sd?1

I had a few questions before I went ahead with the
reassembly:

1) Does it matter which order the disks are listed in when
reassembling the array (e.g. /dev/sda1 /dev/sdh1 ...)?

2) Is there any risk to the data stored on the disks by
merely reassembling the six working disks with the above
command?

3) Does /sys/module/md_mod/parameters/start_ro being
set to 1 prevent the array from syncing/rebuilding/etc.,
or does it only prevent new user data being written to
the array?  If it only prevents user data being written
to the /dev/md*, is there some way to also prevent mdadm
from doing syncing/rebuilding/etc. so I can be sure the
data is not at risk of further damage while testing?

4) Having checked what the "Events" refers to (I thought it
was write-syncing operations before), should I be worried
at the Event count being above 1,000,000?  I have rebuilt
two failed disks and the distro performed a few data
integrity checks on all the disks.  The array is about
nine to ten months old.

5) Any idea why "shutdown -h now" would cause three of
the six working disks to gain 4 events each (happened with
the filesystem unmounted from /dev/md13)?

 - S.A.