Prevent infinite folder replication within home directory
Made my home folder the root data set (/FreeNAS) of my FreeNAS server. This meant my home folder included .FreeNAS/media. I then realized this was silly and made a new data set under the root dataset (/FreeNAS/user). When I switch my user home folder from /FreeNAS to /FreeNAS/user it recursively copied the existing set of data under /FreeNAS into /FreeNAS/user making /FreeNAS/user/media and /FreeNAS/user/user which contained /FreeNAS/user/user/media and /FreeNAS/user/user/user and so on.
This produced around a Terabyte of taken space on my server and required significant effort to penetrate deep enough so the recursively deleting the files wouldn't time out.
I guess from this my suggested fix is that the user shouldn't allow you to make the root directory your home directory and then you need to not be able to change you home directory to dataset inside the dataset that is already your home.