I'll start with a word of caution: Backup everything. Assume you will
lose it.

In any case, when it says stuff about erasing the drive, it's psyching
you out (with good reason): If you are just "reassertting" what is
already there, it won't hurt the data.

Even if you tell it the wrong things, it still won't "erase" the
drive, it only changes the disklabel and maybe the bootblocks if you
install those.

When I was setting up my machine I must have disklabeled and fdisked
the drives 20 times, with no data lose.

The key here is simple: don't mount it as writeable until you are 100%
sure it works as advertised *ALL* the time. It *MUST* work after a
cold boot. Certain things disklabel does, it does to a RAM copy of the
disklabel instead of the physical one, which can be confusing, because
it will work fine, until you reboot.

Make sure you have a disktab set up for the parameters you want,
eveything else is a pain.

Good luck.
--
Hacksaw