On Sunday February 12, mark@xxxxxxxxxxx wrote:
> Thanks for the suggestion, Neil. I had totally overlooked that approach.
>
> So, let's say I can add another physical drive -- /dev/sdc. It's not clear
> how mdadm knows sdc is the 3rd component device for md0. Do you tell mdadm
> to use sdc on the command line as shown below?
>
> mdadm --grow /dev/md0 --raid-devices=3 /dev/sdc1
>
> Or, do you give all three devices?
>
> mdadm --grow /dev/md0 --raid-devices=3 /dev/sd[abc]1
Nether. You just add it as a spare:
mdadm /dev/md0 --add /dev/sdc1
this can be done either before or after you --grow. Once md notices
that the array has room to include another device, and another device
is available, it will start recovery.
>
> If so, then would the revised procedure look like this?
>
> - First, make sure I have a good backup
>
> - Add new drive and partition to be max size of new drive
>
> - Grow the array to be 3 component devices and wait for resync to complete
>
> - Set drive 2 as faulty (e.g. mdadm --manage /dev/md0 --fail /dev/sdb1)
>
> - Remove drive 2 (e.g. mdadm --manage /dev/md0 --remove /dev/sdb1)
>
> - Grow the array back to 2 component devices
>
> But wait, what goes on the command line when you shrink it back to 2
> component devices? Would it be:
>
> mdadm --grow /dev/md0 --raid-devices=2 /dev/sd[ab]1
No, just
mdadm --grow /dev/md0 --raid-devices=2
This will only work (I think) if there are 2 or fewer active devices
in md0, so you do have to fail a device before 'grow'ing down.
Apart from that, this all looks fine.
NeilBrown
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