Disk not showing

Hey all, I just noticed that one of my systems disks isn't showing up in the graph for the disk utilization.

Are there any steps to troubleshoot this?

-- Text from disk status page-- Mon Jan 8 10:04:04 EST 2007 - Filesystems OK

Filesystem 1024-blocks Used Available Capacity Mounted on /dev/sda1 6040288 1035648 4697804 19% / /dev/sda6 69804244 6892104 62912140 10% /home /dev/sdb1 720870988 406581792 277671040 60% /snapshot

Status unchanged in 20 days,18 hours, 9 minutes -- Text from disk status page--