Hello. While this is orthogonal to the task you're working on in this e-mail, I'll note that you'll get much better read-write performance if you create a standard zfs filesystem for your time machine backup, then create a regular file in it which you export via iscsi. I discovered this the hard way after years of wondering why I couldn't get zvols to give me the performance I expected. The performance difference is on the order of 4-5 times beter with files under zfs than with zvols.
-thanks -Brian
