You are reserving space equivalent to one virtual drive.  Uncheck that box 'deny new data writes' and (I am guessing for your tests) the 'ignore reserved space' as well.
I have set up a OneFS 7.1.1 VM 3 months ago.  The entire 17GB of OneFS is filling up even I have only 8.5MB data in it.  How can I clean up the VM to free up some space?  This is a event I see from OneFS Web UI: 2014-12-07 21:11:46 There is at least one smartpool at or over capacity.  Checking on the disk usage, and also directory capacity, OneFS is 103% full, but I only have 8.5Mb data in it (/ifs/data).  isilon-vm-1# df -h Filesystem               Size    Used   Avail Capacity  Mounted on /dev/mirror/root1        989M    450M    460M    49%    / devfs                    1.0K    1.0K      0B   100%    /dev /dev/mirror/var1         989M     70M    840M     8%    /var /dev/mirror/var-crash    1.9G    1.8M    1.8G     0%    /var/crash /dev/mirror/keystore      31M     10K     28M     0%    /keystore /dev/md0                  62M    684K     56M     1%    /tmp/ufp OneFS                     34G     17G   -453M   103%    /ifs isilon-vm-1# du -ch /ifs/data | grep -i total 8.5M    total  Note that there's only 17G in the VM, because I have only set up 3 nodes instead of 6 nodes.  Not sure if this matters: I once upgraded the VM from OneFS 7.1 to 7.1.1.  I have deleted the tar.gz already, but I'm not sure if there's anything else I need to delete to free up space.
How to clean an over-capacity OneFS 7.1.1 VM?