On 05/05/20 09:11, Stefanie Leisestreichler wrote:

Hi.
I want to test if grub is installed on both of the HDs which are part of
my raid1 array. I wonder which would be the best solution to do so.

I think I will archive that when I shutdown the computer, make /dev/sda
powerless and see if it is able to boot from /dev/sdb.

If it is not booting /dev/sdb will have no changes, I would shutdown,
connect /dev/sda with power again, turn it on and do a "grub-install
/dev/sdb". Depending on the state of the array (I guess it will need
recovery) I would do a "mdadm /dev/md0 --add /dev/sdb1". After recovery
I would try it again.

If it is booting from /dev/sdb this HD will have "more" data because of
the one boot process than /dev/sda.

Why? If it boots to the grub menu, just hit an arrow key to stop the
timeout, and then hold the power button for 5 secs to shut it down again.

I am not sure if it is a good idea
to shutdown and just connect /dev/sda with power again, boot (assuming
/dev/sda is the standard boot medium) because I do not know in which
state the array will be. What to do in case I do not want to loose data
from the last boot process with /dev/sdb?

Which would matter why? If you're worried about downloading mail etc,
just kill the network temporarily.

Change boot medium to /dev/sdb
and do a "mdadm /dev/md0 --add /dev/sda1" to get it recovered again
without loosing the "added" data (i.e. in /var/log) from booting? Also
device identifiers could change I guess. Even if I am fine with loosing
the "added" data from booting with /dev/sdb, will - when booting again
from /dev/sda - /dev/sda be the master in the array again?

It is not clear to me if I understood correctly in which case which
array member will be the master which will be the base for recovery. Is
it always the HD one booted from?

The "master" if recovery is required will be the "older" one - in this
case sda because it was disconnected. HOWEVER. Just check whether you
have a bitmap or journal enabled. You can't have both at once, but the
result should be that sda rejoins the array cleanly, raid has a record
of which writes occurred while it was offline, and it will be updated.

Could you please help me with that?

Thanks,
Steffi

Cheers,
Wol