How To control zfs debug messages
Print the debug messages:
echo '::zfs_dbgmsg' | mdb -k
Clear the debug messages, will be realy cleared on next insert (DilOS extension):
echo '::zfs_dbgmsg -Z' | mdb -kw
Change the capacity of debug messages (default == 4MiB, example for 1KiB)
echo 'zfs_dbgmsg_maxsize/W 1000' | mdb -kw
Disable the debug messages