It only needs root read not write. There are a number of ways to do this, including a backup client that only sends data but doesn't write, a read only bind re

It only needs root read not write. There are a number of ways to do this, including a backup client that only sends data but doesn't write, a read only bind remount, or an lvm read only snapshot. The last one is best I think. Make the new lv device readable to the backup user and have it mount it, then copy the data.