UFS smoke test

So my current setup is:

* My home NAS server: Mac Mini running FreeNAS (which is based on FreeBSD)
* 2 x Buffalo DriveStation Duo (USB2.0) with 2 750Gb drives each, connected to the abovementioned Mac Mini. They are just standalone drives, no RAID, so I'm sorta worried, hence Drobo.

I mean to migrate date from those drives to Drobo (one drive at a time)

So the first smoke test: I'm slipping a couple of spare 250Gb drives into Drobo, hooking it up to Mini (lovingly nicknamed "Brick"), formatting Drobo as UFS (FreeBSD's native filesystem) and copying a 50Gb bunch of data to it. Then deleting it and copying again. Lather, rinse, repeat five times. The theory is that the Drobo will not recognize that the data has been deleted, and at the end of this excersize it will think it's 100% full (5 x 50Gb = 250Gb. With only two drives, Drobo has only one drive's capacity, as the other one is used for redundancy.)