1: DriversOne of the first things you need to consider before making any purchasing decisions is whether the server you're interested in offers the necessary driver support. You shouldn't have any trouble getting Windows drivers as long as you're purchasing a server from one of the major manufacturers, such as Dell or HP. However, Linux drivers may not be as readily available. Taking a little time up front to make sure that you can get drivers for your intended operating system can save some heartache down the road.
2: RedundancyIf the server you're purchasing will be used for a mission-critical purpose, you need to make sure it uses redundant parts to avoid having a single point of failure. For example, the server should have at least two power supplies so that if one fails, the other can take over without the server going offline.
Some servers let you install a complete set of redundant memory, while others might include an extra slot you can use to install a spare memory module. The spare memory is used automatically if a memory failure occurs.
3: Hot-swappable componentsIn the 24/7 world of IT, taking a server down for maintenance practically requires an act of Congress. Try to make sure that the server you choose uses hot-swappable components. Granted, not every component is hot-swappable. For example, you can't swap out a system board or a CPU while the server is running. However, many servers support the use of hot-swappable hard drives, expansion modules, and power supplies.
4: Form factorIt should be fairly obvious that you need to consider the server's form factor when making a purchasing decision, but given the importance of choosing the right one, I wanted to go ahead and mention it anyway.
If you're purchasing a rack mount server, make sure that you have sufficient space left in your rack. Remember that 2U and 4U servers require more rack space than a 1U server does. Likewise, if you are planning to purchase a blade server, ensure that you have adequate space left in the blade server chassis.
5: Fault tolerant memoryAnother thing you should look for when purchasing a new server is support for fault tolerant memory technologies, such as Error Correcting Code (ECC). ECC memory can dynamically correct single-bit memory errors. ECC memory can also detect (but not correct) double-bit errors.
6: StorageServers vary widely in terms of available internal storage. Although most of the servers on the market allow for the use of two internal hard drives, there are major exceptions. Some servers don't include any internal storage and may boot from a SAN instead. On the other hand, some of the larger form factor servers include support for large internal storage arrays.
Blade servers typically support only two internal drives, but storage can be expanded through a storage module, assuming that there is sufficient room in the chassis.
7: CPU supportYou should also consider the server's CPU architecture. I'm not talking about Intel versus AMD (although that can be important, too). I'm talking about leaving room for future growth. Many of the servers on the market today offer multiple sockets that can support various types of processors. Organizations typically make a purchasing decision based on how many processor cores they need right now. However, it's a good idea to purchase a server that will allow you to add CPU cores down the road should the need arise. For example, you might start out with quad-core CPUs and then upgrade to six-core or eight-core CPUs later on. Likewise, you might initially fill one CPU socket but add another CPU when necessary.
8: ConnectivityIt's easy to overlook network connectivity when purchasing a server because every server on the market includes built-in networking. However, network connectivity becomes far more important if the server is going to act as a cluster node or as a virtualization host server. Clustering and virtualization typically require more network adapters than a stand-alone server does. In such cases, a server probably won't have a sufficient number of network adapters by default, but you need to make sure it has the capacity to accommodate the additional required network adapters.
9: Memory capacityIf you plan to use your new server as a virtualization host, consider the amount of memory the server can support. Memory is the single most important resource in a virtual server environment, so you must ensure that the server includes enough memory to support all the guest operating systems without skimping on memory.