Ran into an annoying problem, have been having this problem multiple times in the past, and never remember what the fix is. So now it’s on the blog for the next time that I need it. Use the shell option in the FreeNAS installer, the disks that I wanted to install onto was ada0 and ada1.
1. sysctl kern.geom.debugflags=0x10
2. dd if=/dev/zero of=/dev/ada0 bs=512 count=1 && dd if=/dev/zero of=/dev/ada1 bs=512 count=1
This will wipe out the sectors that keep the partition schema and afterward, you can install FreeNAS without problems.