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I suppose this isn't a best practice, but I find myself in a situation where I have zfs filesystems mounted on other zfs filesystems. For example:

zfs list:

...

storage/jayd

storage/jayd/home

The problem I have encountered is that on reboot, the zfs filesystems sometimes mount out of order, and I get an error message similar to:

cannot mount /storage/jayd: directory not empty.

Which indicates that the storage/jayd/home filesystem was mounted before the storage/jayd filesystem.

If you find yourself in a similar situation, the following script may be of use. Disclaimer - make sure you understand what this script does and before attempting to use it ! I take no responsibility for any loss of data that may occur. That being said, I find this script to be useful for sorting through mount issues associated with large numbers of zfs datasets. Note that the script uses 'echo' to display the recommended commands to be executed, but does not actually perform the umount/rmdir commands.

#!/bin/sh
#
# ZFS mount cleanup script.
# Author: Jay Danielsen
#
# Notice: No guarantees - Use at own risk!
#
# Build list of filesystems that cannot be mounted.
for i in `zfs mount -a 2>&1 | grep "^cannot" | \
  awk '{print $3}' | \
  sed -e "s;':;;" -e "s;';;"`; do
  echo $i
  echo cleanup for filesystem $i
  echo "Please verify the safety of the following umount/rmdir commands before executing:"
  # Unmount and rmdir all subdirs
  for f in $i/*; do
    echo umount $f
    echo rmdir $f
  done
  echo ""
done
echo zfs mount -a