You can, to some degree, do an online defrag with zfs rewrite -P now although it is not the primary intent. The displayed fragementation may not go down or may

You can, to some degree, do an online defrag with zfs rewrite -P now although it is not the primary intent. The displayed fragementation may not go down or may even increase, but all the files will go through the allocation policy. zfs fragmentation display is a little misleading, it measures free space fragmentation.