On Mon, 7 Feb 2011 17:32:48 -0800 Jeff Klingner <klingner@xxxxxxxxxxxx> wrote:
> >>>> Also, if you want two rotating backups I would create two stacked raid1s.
> >>>>
> >>>> mdadm -C /dev/md0 -l1 -n2 -b internal /dev/main-device /dev/first-backup
> >>>> mdadm -C /dev/md1 -l1 -n2 -b internal /dev/md0 /dev/second-backup
> >>>> mkfs -j /dev/md1
>
>
>
> On Feb 7, 2011, at 5:19 PM, NeilBrown wrote:
> > I'm surprised that you found the correct advise, and chose not to follow
> > it .....
>
> Thanks again for your advice. I didn't search the list until after completing my initial setup; my mistake and my lesson learned: research first.
>
> > The array you will end up installing on is (slightly) smaller than than the
> > array you have created. So no: you cannot re-arrange things - you have to
> > start again.
> >
> >
> > (well, to be honest, it is possible that you could resize whatever is on the
> > array and then build the secondary array and make it work. But that path is
> > error-prone and this margin is not large enough to properly describe the
> > process).
>
> Reckless fool that I am, I'm going to try it anyway. Here's my rough plan:
>
> 1. Degrade the 3-disk raid1 array by removing two disks, leaving only one, and leaving the array running.
> 2. Set up the first 2-disk array (md0 in your description) de novo on the two freed disks
> 3. Move my data from the original raid1 array (with only 1 of three disks present) to the new 2-disk md0 via lvm mirroring
Nope. That would be wrong. You need to create both mirrors before moving
any data.
So:
3. Set up the second 2-disk array (md1) as a degraded array containing
only md0 as a member:
mdadm --create /dev/md1 -l1 -n2 -b internal /dev/md0 missing
3a. move my data from the original raid1 to the new md1 using pvmove
> 4. Free the third disk by finally taking down the original raid1 array
> 5. create the second 2-device array (md1) using md0 and the freed third disk. Somehow ensure that the md0 component has primacy for syncing.
Then step 5 becomes:
5. Add this newly freed disk to the degraded md1:
mdadm /dev/md1 --add /dev/whatever
NeilBrown
>
> Jeff
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