The easiest way to add lots of storage to any network is to install NAS, or Network Attached Storage. Cisco’s NSS Series of NAS enclosures is available with different numbers of drive bays, with or without the drives themselves. The arrays make it easy to provide a network with up to 12 terabytes of storage.
I recently wrote about Drobo RAID storage arrays. They provide expandable storage with redundancy for the safekeeping of your data. The units that I reviewed are all available with instant savings from B&H until the end of June, 2010. I've just been made aware that there is an 8-bay unit that comes with free hard drives.