It is common to find corporate networks with some servers suffering from storage overload and a lack of spare processing power, while other servers have surplus capacity.

Many companies cope by adding yet more resources in the over stretched areas, but Motherwell College in Scotland decided that better management would offer a more cost-effective solution.

Its answer was a server cluster - with multiple servers able to run the same services - and a storage area network (San) to allow all the servers to access the same pool of storage.

"We had 11 servers on the network for various functions: for example, a staff post office, file stores, printing and so on," explained John Morrison, the college's network systems manager. "After Christmas 2000 we experienced performance issues with the staff server, with disk space becoming critical."

Other servers were doing less important jobs and had spare capacity but, because the storage was server-based, they could not take work from the overloaded system.

"I had seen a cluster presentation at Novell's Brainshare event so I started to think about the extra flexibility and disaster recovery it could offer," said Morrison.

"So I invited Compaq in to discuss the requirements and talk to us about Windows 2000 clusters, Novell clusters and mirroring on Raid. The idea was to build a cluster. We have two buildings 500 metres apart, so we could put two nodes in each and use mirrored storage for disaster recovery."

Migrating services

The discussion with Compaq's consultants made it clear that Windows clustering would not meet Motherwell's needs. At the time, it was limited to two nodes per cluster, and all the resources on a failed server had to go to the other node.

"But with Novell clustering, the cluster could include more servers, and services from one could be farmed out to several others," said Morrison. "You can also migrate services without a failure, to balance the cluster."

Also, Windows 2000 could not do software mirroring over 500 metres and, at £250,000, hardware mirroring was too costly.

Morrison's team decided that Novell NetWare Clustering was the best choice, so it embarked on a proof-of-concept test with Compaq's help. It found only one problem, which was that 12-disk arrays were difficult to mirror.

Three-disk solution

The solution was to reconfigure the storage as arrays of three disks. It meant the college lost some capacity but the result was still cheaper than hardware mirroring.

The cluster comprises four servers: two existing Pentium III systems that were reused, and two Compaq 5500s. Each has mirrored boot drives, plus a third drive as a hot spare, redundant power supplies and 1Gb of memory.

"The servers were specified so that if necessary two nodes could run everything," explained Morrison. To decide how much capacity they needed, the team identified how much disk space was in use and then doubled it.

"The rest of the budget went on four Compaq RA4100 Fibre Channel Raid arrays," said Morrison. "We bought 48 36Gb disks, and we have two RA4100s in each building with 12 drives each. They are software-mirrored between buildings and also configured as Raid 5 at the hardware level."

Morrison is delighted with the result. "We have a lot more flexibility," he said. "You don't need downtime to apply a service pack; you just move that node's services to other nodes before you start work."