If I may continue along the same vein. There is such an option but I do have some obstacles in the path to success. As mentioned earlier I wish to boot FreeBSD from an external drive which involves installing FreeBSD there. Now the main disk runs Windows 10, [AMD CPU]. I have been able to boot the system to the Livefs of the vers. 11 Release which I used as a surrogate prior to installation.
A ls -aqxF /dev/ad* shows the following
/dev/ada0p1 ; /dev/ada0p2 ; /dev/ada0p3 ; /dev/ada0p4 ; /dev/ada0p5
[presumably the internal disk]
There is no other /dev/ada1p'n' etc.
There is a /dev/da0 and a /dev/da0s1
There is also a number of /dev/usb/ entries
I had formatted the ext, drive previously with windows file manager to a single partition, but as the disk, is not obvious to me I have no way of directing the installation, without overwriting the internal disk.
I should add that gpart show does confirm my suspicion of the internal drive as the /dev/ada0 drive and /dev/da0 as the external disk with a ntfs single partition - OK I'll go ahead and try to format this.