Ars Technica has an interesting article on the background of SANs, how they work and how Isilion SAN systems work.
We’ve gone far afield of the original subject here, so let’s swing back to it. As I said a few paragraphs back, Isilon makes a scale-out NAS product that you’d use to hold files. What makes Isilon different from other NAS systems, though, is that it’s particularly suited for providing very fast access to very large files, which makes it a shoe-in for the entertainment industry and for other areas where you need to manipulate big file-based data sets.
An Isilon system consists of a minimum of three Isilon nodes, each of which are individual servers running “OneFS,” a heavily modified FreeBSD derivative, and connected to each other through a fast private IP network. Instead of Ethernet, this private network uses Infiniband for its transport, which Isilon chose because of the extremely low latency it offers versus traditional Ethernet. Unlike a regular SAN or NAS, the nodes all work together in a grid to present a single volume, equal in size to the aggregate capacity of all the nodes’ disks. As nodes are added to the system, their capacities are seamlessly added to the one big volume, without the need to futz around with RAID groups or LUNs or mapping or masking or storage pools or anything else, really. This one single huge volume is Isilon’s core feature—even with all the features and tools that an enterprise NAS system gives you, there aren’t many NAS systems that can present a single, unified multi-petabyte namespace.