external RAID device

[John O'Loughlin]

hello
I have just attached an external RAID device to a redhat box (via a scsi
card). When i run fdisk -l it sees it as /dev/sda. there is a partition
on it already, /dev/sda1. I want to create a new partition, I tried
fdisk /dev/sda and then the usual but was told there were not enough
free sectors. Its a big box so there are. Any suggestions as to what i
am doing wrong would be most welcome. 
John