Want to test the write speeds on your ZFS array?

An easy way to do this is:

time (mkfile 100g /tank/foo)

You will get an output looking something like this:

real    5m01.332s
user    0m0.335s
sys     0m37.958s

To calculate how many MBytes per second the write was, you can use the following formula:

number of MB (102400)/number of minutes (5)/60  = MB/s (in this case it would be 341.34 MB/s)