I had 3, 2TB disks in a RAID5 that I expanded to a 5, 2TB RAID5 (details here). This all went fine but when I went to the folder I have array mounted to (/var/media), it only show 3.5TB of space available. When I check the raid out it shows the correct capacity at 8TB and shows it mounted at the correct mount point (/var/media). What's going on here? What else do I need to do?
While you grew the raid set, you haven't expanded the filesystem mounted on that drive.
Check resize2fs (if it is ext3) or the appropriate tool for the filesystem you have on that drive. Most can be grown in place without reformatting.