Quick Fix
On step 3 be sure to replace ‘/dev/ada4′ with your drive reference. In the ‘view disks’ tab it will be the ‘name’ prepended with ‘/dev/’.
1. Login via SSH
2. sysctl kern.geom.debugflags=0x10
3. dd if=/dev/zero of=/dev/ada4 bs=512 count=1 && dd if=/dev/zero of=/dev/ada5 bs=512 count=1
4. Log into web interface and use “View Disks” to wipe the drives in that interface
5. Create new ZFS volume including these disks.