Failed to start mysql after moving to new partition
Posting this as an answer.
It was a file permissions issue. U need to ensure that the mysql user has access to the mysql datadir and the directory it is in, all the way to the root level directory.
If multiple users need access to these directories, then put them in a group and then give that group access to those directories.
Why don't you just put the ZFS dataset in the location MySQL expects?
zfs set mountpoint=/var/lib/mysql tank/mysql
Now you don't have to worry about strange permissions on /tank and everything looks normal to the rest of the system.