You should almost never use the 'format' subcommand within the 'format' utility.
Why did you pick it?
Just use 'partition' to put the slices like you want.
While you probably shouldn't use it, I don't know why it would make a disk disappear. It's possible that you'd need to power-cycle the disk or possibly even reboot the server, but I can't say I've ever seen that happen.
--
Darren