Riverbed's Steelhead swims through WAN bottlenecks

IT managers are always being asked to do more with less. When it comes to WAN links, less is sometimes all you have to work with. The Steelhead 2000 WAN acceleration appliance from Riverbed Technology is part file cache, part proxy, and part TCP optimization, providing a unique and extremely effective way of reducing the time spent transferring files from one office to another. In addition, the Steelhead is easy to install, and it does not require any LAN/WAN re-engineering. But like other WAN acceleration appliances, a unit must be installed on each end of your WAN link.

Steelhead sits transparently on the LAN between your firewall and your servers. As files and other TCP traffic pass through it, Steelhead automatically analyzes the stream. A technology developed by Riverbed called Scalable Data Referencing breaks the data into indexed chunks and stores it in a local disk cache. The power of Steelhead kicks in when you pass the same or similar traffic back through the appliances over the WAN. Steelhead recognizes the patterns, finds matches in the data store, and sends only a reference pointer for each chunk of data to the other side. There, the reference pointer is used to rebuild the traffic on the fly so that the TCP stream arrives intact. By sending only a small pointer and not the whole file, the appliance greatly increases perceived performance over the link and dramatically reduces the time spent waiting for the data.

Silent Runner

Installing the Steelhead is a no-brainer. Other than setting the IP addresses for the network interfaces through the unit’s browser-based GUI, there is not much to configure. In fact, Steelhead pairs will automatically detect each other over the network. By default, Steelhead will try to optimize all inbound and outbound TCP traffic, but you can select types of traffic to ignore. It also supports layer 4 switches and custom QoS mappings, allowing you to take advantage of your current traffic management policies.

Depending on the model, a Steelhead appliance can have anywhere from 40GB to 500GB of local disk space for caching segments. The Steelhead 2000 I tested came with 135GB of disk space and boasted a maximum throughput rating of 3Mbps. There is no practical limit to the size of the cache — in a perfect world your disk cache would be infinitely large so that you would never have to purge any stored data. Data stored in the cache persists even when the appliance is turned off.

Steelhead uses a dual-port Ethernet card. If the Steelhead software fails, or the unit suffers a hardware or power failure, the two ports will short between them, allowing network traffic to pass unimpeded. You can have two Steelheads in line with each other, with one configured as a slave. The slave unit will automatically take over should the master fail, but WAN users might experience a brief performance hit while the slave builds its segment cache from scratch. Riverbed currently provides no way to synchronize masters and slaves, but future transparent prepopulation is planned.

File caching  systems from companies such as Extreme Networks and Network Appliance have been around for quite some time. Where Steelhead improves on traditional file caches is in its use of indexed file segments. For example, most file caches can reduce the amount of traffic traveling over a WAN link only when the files requested have been cached on both sides and, typically, only if the files have not been changed or renamed. Frequent changes to files can significantly limit their effectiveness.