Shared-disk clusters make the most efficient use of storage resources, but the software is more complex. Be sure the hardware and software components are tested and can work together. The list includes servers, storage and networking. To minimize tuning requirements, choose uniform hardware configurations on all servers. Be sure the applications are compatible with the clustering server.
Redundancy is important.
Use multiple network interface cards, hubs and power supplies, and implement RAID and uninterruptible backup power supplies to eliminate single points of failure. Identify the applications to be clustered and how much of a load they'll put on the server . Mission-critical applications are the ones you want to cluster. Take into account memory, disk, CPU and network utilization under a variety of different client loads. Account for future growth.