always fails

Fails with errors:

    mdadm: /dev/loop0 is smaller than given size. 18976K < 19968K + metadata
    mdadm: /dev/loop1 is smaller than given size. 18976K < 19968K + metadata
    mdadm: /dev/loop2 is smaller than given size. 18976K < 19968K + metadata

    ERROR: /dev/md0 isn't a block device.