Blade servers are a Good Thing, and that's with capital letters. I've been using and writing about blade servers for about four years now, and the combination of scalability, performance, low power consumption and heat dissipation, manageability and sheer convenience is unlike anything else in the data center.

Blade systems excel in applications ranging from Web server farms to high-performance computing to Software as a Service hosting. When used in conjunction with load-balancing hardware or virtualization, they make the task of deploying processing capability literally as simple as plugging an 11-pound server blade into a rack-mounted chassis. With the advent of Opteron-based blades, such as the IBM BladeCenter chassis and a couple of brand-new LS20 server blades that Big Blue recently loaned me, a new benefit is added to the blade pantheon: AMD64 technology.

What's a Blade Server?
Let's start by talking about a traditional low profile "pizza box" dual-processor rack-mount server. You can stuff 42 of these 1.75-inch-high servers inside a standard server rack (which is therefore referred to as 42 rack units, or 42U, high). Each 1U (one rack unit) server contains its two processors, memory, main logic board with chipset and bus controller, hard disk controller and drives, Ethernet controllers, and other assorted goodies. That's what makes the server a server. Each traditional server also contains support hardware, including power supplies, cooling fans, and other components that take up a lot of space, generate a lot of heat, cost a lot of money, but don't contribute to processing, storage or connectivity.

The premise of the blade server: Remove all that support hardware, the power supplies and fans and the like, from the server. Put them into a box, called the chassis, which can hold, say, fourteen servers. In fact, let's consolidate the gear to gain economy of scale: Rather than having 14 500-watt power supplies for 14 traditional 1U pizza-box servers, let's have two 2000-watt power supplies. Ditto for cooling. This not only reduces the number of parts and saves space, but also reduces the amount of cabling required.

With all that support gear removed and put into the shared chassis, we can make the server itself—the processors, memory, logic board, storage, and connectivity—much smaller. This reduced-size server, now called a server blade, can be hot-plugged into the chassis, which provides the power and cooling. The chassis also provides built-in network connectivity, including switches, to further reduce cabling, and a centralized management system. The result: The server blade itself contains only the stuff needed to be a server. All the other support stuff is put into the shared chassis.

Figure 1. The Front of the IBM BladeCenter Chassis. You can see one LS20 blade on the left, and then a space where I remove the second blade. Above the blades are the floppy and DVD drives, a shared USB port, and a few status indicators.

Overall, there's a net savings not only of space, but also of power and cooling. In the IBM BladeCenter system, you can install 14 dual-processor servers into a chassis that's only half the size that 14 traditional pizza-box servers would require: 12.25 inches instead of 24.50 inches. That's right: 14 dual-processor servers, each with two hard drives and up to 16GB servers in a box about a foot tall (about the height of my microwave oven, in fact). That gives you 84 dual-processor servers, not 42, in a full-size rack.

Beyond increasing the server rack density, I mentioned some other significant benefits of server blades. Power is a big one—a blade server might only consume half or two-thirds the power of a traditional rack-mount server of equivalent processing power. That results in less heat, and therefore, less power spent on server-room cooling. There's the reduced cabling, of course, and also easier installation and maintenance. If you've struggled to install or swap out a traditional rack server, you'll appreciate how a blade server just snaps into place. Management is also a big issue—all the major server-blade makers include management software that lets you administer a chassis as a single unit, and also hot-swap blades in the event of a failure. And cost: Though you have to spend some up-front money on the chassis, a server blade is typically less expensive than a similar standalone pizza-box server.

Wow. Now you can see why I like blade servers. So, now let's talk specifically about the IBM BladeCenter chassis and the new LS20 Opteron-based server blade.

The BladeCenter Chassis
I've already described the basics of what the BladeCenter chassis (Figure 1) is: It's a 12.25-inch box that, from the front, contains as many as 14 slide-in server blades—if you don't fully populate it, you install covers that maintain system integrity and help guide airflow. The front of the chassis also has floppy and DVD drives that can be accessed by all 14 servers.

From the back (Figure 2), the BladeCenter has a wealth of shared gear: up to four hot-swap power supplies, cooling fans, and four communications module ports, which can contain any combination of Gigabit Ethernet and Fibre Channel switches. The system I tested contained one GigE switch and two power supplies. Between the front and back of the server is the active midplane board, which is what the servers plug into, and which provides the connectivity for the blades (as passed through the midplane board) and the chassis' management module.

Figure 2. The Back of the IBM BladeCenter. On the left, switch modules; in the middle, cooling vents, which are closed because the server is turned off; on the right, management system with keyboard/video/mouse connectors. There are two power supplies on the right; two more power supplies can be inserted on the left, next to the switches.

What about the blades? IBM has long offered a variety of plug-in servers, which you can mix-and-match. About three years ago, I reviewed the BladeCenter for InfoWorld using the HS20 server, which had dual Intel 2.6GHz Xeon processors, 768MB RAM and a single 40GB hard drive. Today, IBM has broadened the offerings, also now offering an HS40, a double-width server with four Xeon chips; the JS20 and JS21, which use IBM's POWERPC processor; and now the exciting LS20, which can use one or two Opteron processors, can contain up to 16GB RAM, and as much as 146.8GB of internal high-speed storage. No other company offers this much flexibility— and no blade is as versatile as the LS20.

The LS20 Server Blade
Figure 3 shows the inside of the LS20 blade. The two copper rectangles on the left are the heat sinks for the two AMD Opteron model 275 processors; IBM currently offers a range of chips from the model 246 to the model 280. Above and below the processors are four DIMM chips, offering up to 16GB RAM. The test systems I had each contained 4GB RAM. Top right: the two hard drives, available in sizes up to 73.4GB each; that's what IBM provided for me.

Notice what's missing? No power supplies, no fans. That's all provided by the BladeCenter chassis, which makes the servers light and small. On the right are two multi-pin connectors, which plug into the midplane when the server is inserted into the chassis. Those provides all the connections for power, networking pass-through for the dual on-board Gigabit Ethernet NICs, hookups for the chassis' floppy and DVD drive, and management.

Unlike many other companies, IBM blades have internal expandability beyond memory and storage. The beige connector below the right-hand hard drive is for an accessory daughter board, which could be used for Fibre Channel, InfiniBand, or any number of other options.

Figure 3. The Inside of the IBM LS20 Server Blade. The inside of the IBM LS20 server blade, with processors, memory, drives and lots of chips. There's normally a cover over all these parts.

One final item I'd like to point out on the hardware: On the bottom, directly under the left-hand hard drive, you'll see what looks like a chip with a blue button. That's IBM's unique LightPath diagnostic display. If a server blade fails, you can remove it from the chassis, sit it into a desk or test bench, remove the cover and press that blue button. Diagnostic indicators on the LightPath chip will then indicate what went wrong.

From the user perspective, the LS20 is just like any other dual-processor Opteron server: It's fast, stable and reliable. One of the servers that IBM provided has 64-bit Windows Server 2003, and the other had 64-bit SuSE Linux; both worked like a champ. But remember what I mentioned about power? The Opteron processors in these servers draw a maximum of 68 watts per chip – significantly below the power used by a standard Opteron processor – but with the same performance. That lets all 14 servers (and the chassis and switch modules!) run with two 2000-watt power supplies – that is, no more than 285 watts, net, for a dual-processor 64-bit server with up to 16GB RAM and 146GB of storage.

What's not to like? That's why blade servers are a Good Thing, and why the BladeCenter with the Opteron-based LS20 server blades is a Really Good Thing.