Bladed servers are all the rage in IT departments around the world. Manufacturers have developed a whole line of fantastic bladed server devices designed for service provider and high-density enterprise applications. However, it is important to understand that these systems have both advantages and disadvantages that must be considered before IT managers place an order.

The demand for these systems is based on manageability, ease of deployment and efficiency of space utilisation. All three of these needs are met with bladed systems. The console management and remote power control of these systems are powerful, and getting better. Corporations managing hundreds or thousands of servers enjoy the consistency and ease of these new bladed deployments. Companies with rapid growth, in particular Internet companies, have found that bladed systems deploy faster and with less installation troubles than alternatives.

At Equinix, where eight of the top 10 Web properties in the US host their gear, there is an increasing number of deployments of these systems, but they tend to be used by the less Internet-centric organisations. In any modern data centre you will see various examples of these bladed systems, though most are still experimental and for smaller applications at this time.

Part of the slower adoption of these high-density systems are because bladed solutions are not for everyone and every application. There are a number of reasons why bladed servers might not be the best solution for some organisations.

For example, one large Internet search engine that considered deploying bladed servers chose a large-scale 1U server deployment instead. For this company, the added advantage of having individual devices, where a single device failure would not take down an entire bank of servers, was critical.

With bladed server systems, multiple CPUs rely on a single device, increasing the risk of potential failure. In this case, the manageability is exactly the same as bladed servers - the company uses identical 1U boxes with common management, console and power cycling tools. However, the servers are much less expensive per CPU, and in theory a single server can disappear entirely without affecting the entire system.

A number of financial institutions have taken the same position where deployment is concerned. While rolling out blades is in some ways easier than a high-density rack of 1U servers, failure management is easier to modularise with the 1Us. When determining a cost per CPU deployment, you also must consider replacement costs in staff hours, shipment and equipment. A single blade can cost significantly more than a 1U CPU box. In high-density deployments, the cost per 1U server is so inexpensive that we have seen these financial institutions treat the 1U boxes as disposable devices. They remain "disposed of" until the next scheduled staff visit to the lights-out data centre.

Finally, a common misperception about bladed servers has to do with space efficiency. While it is true that you can fit more individual CPUs per cabinet using bladed servers, the power consumption drastically increases per cabinet. Although some bladed servers do use lower power CPUs, the total power consumption per cabinet is an order of magnitude higher than what is consumed with high-density 1U server deployments.

Because hosting sites charge for power and cooling, the power used and heat exhausted by these bladed systems has increased the costs for data centres which is then passed along to customers. For this reason, bladed servers will not decrease costs per cabinet of deployed CPUs until their total power consumed per CPU has decreased at the same rate as space consumed. Furthermore, some legacy data centres are not designed to accommodate the high power density requirements of bladed servers.

Overall, bladed server technology is a strong addition to today's data centre infrastructure. However, before deploying, IT managers should consider their specific applications and the advantages and disadvantages of managing them on bladed servers. A critical consideration should be the total cost, before during and after initial installation. Finally, consider the power and heat issues of bladed server systems, as most companies have found these systems cost significantly more per cabinet than traditional deployments.

Adelson can be reached at [email protected]