現象

debian8 で zfs を昔使っていた。
その後zfsを使わずext4で使っていた。
debian9 をクリーンインストールした後、blkidでUUIDが表示されないことに気がついた。
dd if=/dev/zero of=/dev/sda bs=1M count=1000 とかしても消えなかったので調査したところ、wipefsコマンドで消せることにたどり着いた。
HDD mount problem (bad FSTYPE) / System Administration / Arch Linux Forums

確認

# wipefs /dev/sda1
offset               type
----------------------------------------------------------------
0x7470abfc00         zfs_member   [filesystem]
                     LABEL: tank500
                     UUID:  7915798765570182767

0x438                ext4   [filesystem]
                     UUID:  d307f4b7-0862-4a5a-bcd3-fbdc3b842c12

消去

# wipefs -a /dev/sda1
/dev/sda1: 2 bytes were erased at offset 0x00000438 (ext4): 53 ef
/dev/sda1: 8 bytes were erased at offset 0x7470abfc00 (zfs_member): 0c b1 ba 00 00 00 00 00
/dev/sda1: 8 bytes were erased at offset 0x7470abf800 (zfs_member): 0c b1 ba 00 00 00 00 00
/dev/sda1: 8 bytes were erased at offset 0x7470abf400 (zfs_member): 0c b1 ba 00 00 00 00 00
/dev/sda1: 8 bytes were erased at offset 0x7470abf000 (zfs_member): 0c b1 ba 00 00 00 00 00
/dev/sda1: 8 bytes were erased at offset 0x7470abec00 (zfs_member): 0c b1 ba 00 00 00 00 00
/dev/sda1: 8 bytes were erased at offset 0x7470abe800 (zfs_member): 0c b1 ba 00 00 00 00 00
/dev/sda1: 8 bytes were erased at offset 0x7470abe400 (zfs_member): 0c b1 ba 00 00 00 00 00
/dev/sda1: 8 bytes were erased at offset 0x7470abe000 (zfs_member): 0c b1 ba 00 00 00 00 00
/dev/sda1: 8 bytes were erased at offset 0x7470abdc00 (zfs_member): 0c b1 ba 00 00 00 00 00
/dev/sda1: 8 bytes were erased at offset 0x7470abd800 (zfs_member): 0c b1 ba 00 00 00 00 00
/dev/sda1: 8 bytes were erased at offset 0x7470abd400 (zfs_member): 0c b1 ba 00 00 00 00 00
/dev/sda1: 8 bytes were erased at offset 0x7470abd000 (zfs_member): 0c b1 ba 00 00 00 00 00
...

確認、再フォーマット

wipefs /dev/sda1
mkfs.ext4 /dev/sda1
blkid

blkid で UUID 値が表示されることを確認。