During the install of FreeNAS, the process may hang with the following errors:
UNMAP failed, disabling BIO_DELETE
UNMAP. CDB ...
CAM status: SCSI Status Error
SCSI status: Check Condition
SCSI sense: ILLEGAL REQUEST ... (Invalid field in parameter list)
Command byte 0 is invalid
Error 22, Unretryable error
This was with both FreeNAS-9.10.1-U2 and FreeNAS-9.10.2-U1 (though it is unlikely that this specific incompatibility is isolated to only these two builds). One thing to try is to first shut down the guest and then reconfigure the VM. For the Hard Disk configuration options of the VM, the default setting for Virtual Device Node is SCSI Controller. Changing it to SATA Controller resolved the error and FreeNAS was able to then install successfully.