If you have the space for storing data twice, you can actually use `dup` for the data, not just the metadata. That conversion can be done online, though I mana

If you have the space for storing data twice, you can actually use `dup` for the data, not just the metadata. That conversion can be done online, though I managed to make it zero out all superblocks on all 3 disks while converting from raid1 to raid5. That's some time back, however, and there was some unfortunate power cycling.