Rewinding: europa:~# df Filesystem 1K-blocks Used Available Use% Mounted on /dev/mapper/array-root 19223252 2342136 15904632 13% / /dev/sde1 474440 43692 406251 10% /boot /dev/mapper/array-store 8630753568 5064478176 3565005632 59% /storage
So basically each of the 1.5tb drives has 2 partitions, small ~500mb for either /boot or swap and the rest for md0 (+lvm on top). The 3 newest drives have the ~500mb partitions unused. So I guess I could cobble totally non raid system, but it will be vulnerable as hell to disk failure. Now that I look at it, I should have put the backup file in /boot, just wasn't thinking the process through properly.
1. Let it take 20 days to reshape with the nfs backup file.
2. Use a live boot, take the raid offline and reshape.
3. If possible, stop the reshape, copy the backup file to /boot and start it up again.
Much rather an easy fix that's safe, but that's not always possible.