By Edmund X. DeJesus
Computerworld |
Transactions per square foot sounds like a unit more suited to paper-and-pencil accountants than data centers. However, packing servers more densely into racks can increase the processing power that each rack and its floor space can provide. This server strategy makes sense for a variety of situations, but it comes with a few caveats to consider first.
New server strategies are supplanting traditional minirefrigerator-size pedestal servers and large, mainframe-style servers by taking advantage of rack mounting. Standard data center racks are 42U high (where U is a form factor measuring 1.75 in., with a standard PC "pizza box" base). Ordinary servers are usually 3U high, meaning a rack theoretically can hold 14 servers. However, by reducing server height to 2U or 1U, a rack can hold 21 or 42 servers—increasing the processing power by 50% to 100% in the same floor space. Data center managers value this increase, and indeed, 1U seems to be the new standard. Major server vendors, including Compaq Computer Corp., Dell Computer Corp., Hewlett-Packard Co. and IBM, all offer 1U servers.
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These aren't skimpy boxes, either. Each 1U server can typically handle one or two processors in the Pentium to near-gigahertz range, up to 4GB of RAM, one to three 20GB hard drives, plus at least two network ports and all the trimmings. Slip 42 of these screamers into a rack, and you're packing a punch.
Naturally, the ability to shoehorn more computing power into a smaller space is one of the prime reasons for considering such ultraslim servers. Data center space is usually at a premium, so any way to make existing operations more compact is welcome. Also, data center space is expensive: The longer you can avoid renting more of it, the better. "This approach also supports incremental increases in server capacity, since you can add to existing racks as needed without large capital investment," says Marc Jourlait, director of Netserver business for North America at HP. Finally, it's easier for staffers to tend servers that aren't spread all over a building.
The RLX System 324 rack from RLX Technologies Inc. holds 14 ServerBlade chassis units, each accommodating 24 ServerBlades, for a total of 336 servers per rack. |
There are other considerations also. "Deploying tens or hundreds of 1U servers in clusters can give you the raw processing power of supercomputer-class machines for a fraction of the cost," says Subo Guha, director of marketing for the enterprise system group at Dell. Without the component bells and whistles of larger boxes, small form-factor servers may use less power, an important consideration lately. The hope is that racks of such servers will permit smaller staffs and save further data center costs.
Despite the undeniable benefits of compact rack-mounted servers, there are other considerations. One is power consumption. Although such servers are typically designed to minimize power consumption—and some companies design their offerings with low-power chip sets originally intended for handhelds and notebooks—there's no doubt that a rack holding 42 servers sucks down a lot of power. This may require rewiring the data center to handle the power needs more effectively. Indeed, depending on the original purpose of the data center space, it may require either upgrading the entire power supply or moving to a different facility.
A rack with 42 two-processor servers throws off a good bit of heat, which must be removed efficiently to prevent component degradation or burnout. This may require special air-conditioning arrangements, rack placement and elevated floors that harken back to glass-house days.
Storage is an interesting challenge, since you typically want each server to have access to whatever storage it may need. (The onboard hard disks are typically for internal needs only.) This will require some combination of direct-attached storage and attachment to storage-area networks. Sorting out all the permutations and complexities may require automated software assistance.
One important consideration usually doesn't become apparent until you actually begin deploying many servers in a rack. With power lines, network connections, storage connections and all the other wiring necessary for 42 servers, each rack begins to look like an explosion in a cable factory. Keep this in mind when comparing servers, since some products may offer special cable-reducing features.
Flashing Blades
A new development in the compaction of servers is the appearance of blades. A blade is essentially a server mounted on a card within a special chassis or shell. The chassis typically provides power and some I/O connectivity in a 3U-high space. One blade can handle one or two processors, typically up to 512MB of RAM, up to three 20GB hard drives and one or two network connections. Since each chassis typically holds six to 12 blades, and each blade can handle up to two processors, standard racks can hold the equivalent of up to 336 servers. That's compact.
Fibercycle Networks Inc. in Los Gatos, Calif., and RLX Technologies Inc. in The Woodlands, Texas, are two of the pioneering vendors in the blade arena. However, most of the major vendors have blade offerings as well, or at least plans for them. Both Fibercycle and RLX use lower-power processors from Santa Clara, Calif.-based Transmeta Corp.
While blades clearly deliver even greater transaction densities than 1U servers, they can also multiply the challenges of deployment. The same considerations of power consumption, heat dissipation, storage connection, cable handling and management all apply, but to a vastly greater population of servers.
One approach to blade deployment is to expand the blade concept beyond servers. Blades dedicated to I/O or storage within the same chassis may dilute the raw processing power of a rack but provide for a more balanced and reasonable solution. "Dell is developing a 'brick' strategy, which would include consolidated access to storage in a more flexible chassis," says Guha. More sophisticated blade shells may also offer a consolidated power supply to reduce the number of heat sources, heat sensors to allocate cooling more efficiently and simple access to blades for dynamic reconfiguration or swapping.
Trends toward smaller form factors in rack-mounted servers are clear. As usual, it's the variations on the theme that are interesting. The 1U or 2U height is becoming the standard, and vendors will undoubtedly move to pack as many processors, hard drives, ports and other goodies into that space as possible. Refinements to reduce power consumption and handle heat will continue to advance, probably with different low-power chip sets and onboard fans and cooling technologies.
Other vendors, like Crystal Group Inc. in Hiawatha, Iowa, are introducing servers that vary in width and depth. The ability to pack three or four servers across and two deep in a 2U or 3U space may appeal to some managers. Look for further experimentation in the width and depth dimensions.
There's also a divergence between general-purpose servers and application-specific servers. For example, servers that are specialized for delivering Web pages are an obvious boon to Internet providers. Expect to see more specialized compact servers for particular niche applications, including files, printing, e-mail, enterprise resource planning, customer relationship management and database access.
Novel server form factors are also bringing new payment models. "HP was the first to introduce payment for what you use, rather than for what you have," says Jourlait. While you may have many servers in a rack to handle peak loads, you pay only for the processing you actually do. That allows an administrator to expand his data center incrementally and grow into the extra server capacity he has on hand. Versions of this model will probably become more widespread.
Compact servers are currently the hottest segment of the server market. "Growth for Dell in this segment was 600% in the past year," says Guha. A recent report from Framingham, Mass.-based IDC indicates that the market for appliance servers will grow from $3.8 billion last year to more than $30 billion by 2005.
Blade servers are poised to become the hottest segment of the compact server segment. The prime customers for these servers are, not surprisingly, service providers, which use them largely to serve Web pages. But major corporations aren't far behind.
"We see small to medium providers and midsize to large corporations that serve their own pages as prime users," says Jourlait.
DeJesus is a freelance technical writer in Norwood, Mass. Contact him at dejesus@compuserve.com.
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Copyright © 2001 IDG Communications, Inc.
