On a disk drive there was ZFS filesystem installed, and now it's been replaced with btrfs. But "zfs_member" label remains as the disk label:
$ lsblk -f sda |----sda1 ntfs label1 sdb zfs_member |----sdb1 btrfs label2
How can this label be removed?
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Probably the ZFS disk label was not wiped by the btrfs format. (I know it happens with MD, because the MD label can be at the end of the drive. Even more exciting if MD auto-activates when you don't expect it).
If you have no files, just use
wipefs and then reformat.
Wipefs is part of the same ecosystem that detects these labels (libblkid, credit Karl Zak). So it should be designed to erase exactly the same labels that are detected.
If you have files and backup+reformat is undesirable, you need to be very careful. Read through the manpage for wipefs, make sure you have a boot disc with dd and a safe copy of the wipefs manpage. And back up user data on all filesystems first :).
E.g. I'm thinking
wipefs --backup. And
wipefs -n first to see what it might do.
wipefs -t to clear the zfs magic only (and not btrfs). ...and if you can unmount the filesystem first to avoid race conditions, that would be a really good plan. Definitely try to get
wipefs --backup saving to a different filesystem than the one you're performing field surgery on.