NAS
A NAS unit is essentially a self-contained computer connected to a network, with the sole purpose of supplying file-based data storage services to other devices on the network. The operating system and other software on the NAS unit provide the functionality of data storage, file systems, and access to files, and the management of these functionalities. The unit is not designed to carry out general-purpose computing tasks, although it may technically be possible to run other software on it. NAS units usually do not have a keyboard or display, and are controlled and configured over the network, often by connecting a browser to their network address. The alternative to NAS storage on a network is to use a computer as a file server. In its most basic form a dedicated file server is no more than a NAS unit with keyboard and display and an operating system which, while optimised for providing storage services, can run other tasks; however, file servers are increasingly used to supply other functionality, such as supplying database services, email services, and so on.
SAN
Put in simple terms, a SAN is a specialized, high-speed network attaching servers and storage devices and, for this reason, It is sometimes referred to as “the network behind the servers.” A SAN allows “any-to-any” connection across the network, using interconnect elements such as routers, gateways, hubs, switches and directors. It eliminates the traditional dedicated connection between a server and storage, and the concept that the server effectively “owns and manages” the storage devices. It also eliminates any restriction to the amount of data that a server can access, currently limited by the number of storage devices attached to the individual server. Instead, a SAN introduces the flexibility of networking to enable one server or many heterogeneous servers to share a common storage utility, which may comprise many storage devices, including disk, tape, and optical storage. Additionally, the storage utility may be located far from the servers that use it.
Comparing NAS & SAN
Look towards NAS as sharing on file level, where you provide access to a filesystem to many by protocols such as CIFS, Samba, NFS, HTTP, … SAN shares a disk on block level, where you should look at it as a raw disk that you share over a network (iSCSI, Fiber Channel, …). It’s a one-on-one relation where the operating system (or application) should take care of the filesystem. (More info)
Demystifying Storage
If you’re looking for a good Open Source product for all your storage needs:
www.openfiler.com
Karim Vaes 