Using ConsoleOne from the administrative workstation, it was easy to monitor cluster resources as they moved automatically or to move them manually from one node to another. Even with several large, complex applications installed simultaneously on the same cluster, a configuration many might not attempt, there were no problems as applications moved from one node to another.

The Windows 2000 Advanced Server, with Cluster Services and Network Load Balancing, is set up using two certified systems--currently a very short list. The servers share storage, either by shared SCSI or Fibre Channel, and communicate with each other via a dedicated network interface or normal data network interface, although that's not recommended. If one server fails, the other starts up the designated applications, and clients can reattach once the applications finish booting.

The installation process for cluster services on Windows 2000 Advanced Server is much easier than that for cluster services on NT Server 4.0. Installation of the cluster and Microsoft SQL Server 7.0 took about half an hour, compared with more than a day for the same task with the previous version running on NT Server.

Time for failover of the application from one node to the other depends on the time it takes for the application to launch. With no large database, SQL Server took less than a minute to move from one node to the other.

Network load balancing is a service for Windows that has some advantages in a Windows shop. It's included with the operating system, installs easily, doesn't have a single point of failure, and is relatively easy to set up and administer. The disadvantages are that it runs on each server in a load-balancing cluster, which means that it's an additional item that must be installed on each node. It works only with Windows 2000 Advanced Server or DataCenter Server (when it ships), and can load balance only those applications running on the server, not external devices such as firewalls.

Network load balancing installs as a network service, just like adding another protocol or VPN. The installation process is simple and easy to configure. It offers standard load-balancing functionality, but not the sophisticated features typically found in dedicated load balancers. If a server in the load-balancing cluster fails, the other servers take over for it, sharing requests.

Windows 2000 and Active Directory provide a simple way to update content to each server in a network load-balancing cluster, making it easier to maintain a Web server cluster, for instance.

For administrators with Unix backgrounds or the willingness to learn Unix, and the need to support highly available and scalable applications, SCO UnixWare Non-Stop Clustering is well worth investigating.

While hardware choices are limited, the next version should considerably extend hardware configuration options and remove the requirement to use ServerNet for interserver communications.

NetWare Cluster Services doesn't require specific hardware certification (just that the servers be the minimum configuration for NetWare), and nodes in the cluster don't even need to be identical. Requirements for shared storage are also broad and easy to fulfill. NetWare Cluster Services is easy to set up for anyone who can install NetWare--it's a much less onerous task than installing UnixWare, for instance. This product is good enough to bring developers back into the Novell fold, but until that begins to happen, applications are limited.

Windows 2000 Advanced Server comes with cluster services and network load balancing at no additional cost. However, failover is limited to two nodes for now, and load balancing is most useful for Web server applications. Scaling other types of applications is less feasible.

All of these products have a place in an enterprise environment. UnixWare offers the feature set closest to the high-end clustering we're accustomed to from the proprietary systems of old. NetWare offers a high number of nodes, and Win-dows 2000 is the platform most developers will create applications for first. It's really up to the IT department to determine its priorities and select the most appropriate platform.