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Since i migrate to zfs where it is possible, i did this also with an usb storage. Today, i want to export a pool to use it in my laptop. I finished all i want to do and want to remove the zpool from my system via

zpool export mypool

. The result:

umount: /foo/bar/mypoo/foobar: target is busy. (In some cases useful info about processes that use the device is found by lsof(8) or fuser(1)) cannot unmount '/foo/bar/mypoo/foobar': umount failed

Ok, maybe it needs some time to finish writing/flushing the cache so i gave him another 15 minutes. I tried again and the same error message. I used "lsof" but nothing inside when i grep for "mypool". After taking a long look over the internet, the only solution i found was using

zpool export -f mypool

but again, same error. After strange threads talking about "you have to restart your usb module" i just took a look to the current running systemd units by using

systemctl list-units

and guess what? There are units running for each mountpoint the zfs pool had. All i had to do is to stop the unites and the run "

zpool export mypool

the last time :-).