Comment 11 for bug 1801349

Some notes:

1. /dev/vdb did appear to have an ext4 file system on it before we created the file system.
2. [jbd2/vdb-8] running implies the file system was mounted at some point on /dev/vdb
3. Nothing seemed to have mounted /dev/vdb

The file system was indeed mounted during boot:

[ 94.945578] EXT4-fs (vdb): mounted filesystem with ordered data mode. Opts: (null)

After a reboot the [jbd2/vdb-8] thread is no longer running and zfs can create the file systems w/o any issues.