You may have to refer to it by the /dev/mapper entry. Are you doing this on the CL or in Yast?
Also, just an aside, but why are you not putting / in the LVM? You can carve out a 90MB /boot and keep the rest maintained by LVM, including swap, or, with recent improvements in speed, put swap on a mounted filesystem as a file, as it will continue to do block I/O to the file.