Shout out to the list regulars for some help on this, while waiting for more information... The short version of my strategy so far is to try to find the 1MiB backup file for the first 1MiB of /dev/md3 that was accidentally zero'd. Virtually certain the 1MiB file we're looking for contains an LVM signature. So that should be straightforward to search for and figure out the offset; hopefully the file is in a contiguous extent, extract it with dd, and then reverse it around and write the file back to /dev/md3. Any tips on how to search /dev/md3 for this signature? Use dd with grep to search for the lvm2 signature? Or testdisk? Another possibility is, if we regain access to the NAS's /etc/lvm, then maybe there's a backup or archive file for LV; and maybe that can be restored with help from the LVM list; and then maybe we're super lucky and it is Btrfs and the system block group isn't in that first 1MiB and therefore all we have to do is restore one superblock (pretty easy) with the help of Btrfs list. Any other ideas? :-D --- Chris Murphy
