You can never have enough storage, whether a bigger house to store your belongings, or more hard disk space to store your data on a network.
Traditionally, storage has been divided into three categories:
DAS (Directly-Attached Storage) - Storage that is directly attached to a computer host (internal bus) like for example internal hard drives, USB memory sticks etc.
SAN (Storage Area Network) – A SAN is two or more devices communicating via a serial SCSI protocol, such as Fiber Channel or iSCSI
IP Storage Servers – Traditionally, installing server-based storage is complicated, expensive, and requires you to take down the server, shut down the server, install disks, reconfigure software, set share privileges, and restart the system. But these aren’t problems with Network Attached Storage (NAS Server). IP Storage Servers connect directly to a network, and is as easy to install as plugging a telephone line into a wall jack. You generally don’t need to add software to make IP Storage Servers run, and configuration is minimal.
An IP Storage Server is a server that is dedicated to file sharing. IP Storage Servers do not provide any of the activities that a server in a server-centric system typically provides, such as e-mail, authentication or file management. IP Storage Servers allow more hard disk storage space to be added to a network that already utilizes servers without shutting them down for maintenance and upgrades. With an IP Storage Server, storage is not an integral part of the server. Instead, in this storage-centric design, the server still handles all of the processing of data, while an IP Storage Server delivers the data to the user. An IP Storage Server does not need to be located within the server but can exist anywhere on a LAN, and can be made up of multiple networked IP Storage Servers.
Information courtesy of Thecus® (http://www.thecus.com/storage_general.php?set_language=english)
