Today, 1U and 2U rack-mount servers are short in height and slim in width, but the space savings is counteracted by increasing server depth, which takes up valuable data center floor space and crowds racks, data center managers say.
"The 1U servers that seem to be growing to absurd depths," Chuck Goolsbee, a VP of technical operations at the Seattle-based colocation facility Digital Forest Inc., wrote on the SearchDataCenter.com blog. "Every time a new server appears on the market, the very first spec I check is depth. . . . The makers of gear destined for the data center seem to think they've been given a free pass [to] go as deep as they please. This drives me, and I can only assume my peers in the community, crazy."More than an annoyance
By 2002, Goolsbee began noticing greater server depths and became particularly concerned with the upward-depth trend when a colocation customer recently sent a new Apple Xserve to replace its previous Apple G5 unit, and it was too deep to fit in the rack. Making matters worse, Apple swapped the positions of the Ethernet and power cable positions on the new server, so cable management was also a headache, Goolsbee said.
"Both [I] and the customer thought this would be an easy swap: power down, unplug, and pull out the old one, slide in the new one, plug in and power up, [with] minimal downtime," Goolsbee said. "Unfortunately, the new one is two inches longer, the ports (network and power) have swapped sides, and the rack-mounting hardware is completely different. What should have been a five-minute operation turned into a multihour ordeal. It's like they tried to reinvent the wheel with a new server and didn't think about what that means."
The previous-generation Apple Xserve G5 was 28 inches deep. On Apple's Web site, the company states that with the Xserve, "there's no need for a special 'Apple rack.'" You can install the server in any of several types of racks, including open four-post rack and cabinets from 24 to 36 inches deep."
When asked about the additional length, an Apple spokesperson replied, "The industry-standard rack is typically 36 inches deep and 30 inches post to post, so we fit right into the standard rack space without issue. The slight depth increase does not change the effective density of the 1U server."
Another of Goolsbee's colocation clients shipped 32 Dell 1950 servers to Digital Forest, along with an APC NetShelter cabinet and power strips to plug it all in. The 30-inch deep servers and power strips fit in the cabinet -- as long as the cabinet door remained open, Goolsbee said.Industry x86 server depths
The earlier-generation 1U Dell PowerEdge 860 servers were 21.5 inches deep, followed by the deeper 24-inch PowerEdge, SC1435. Calls and emails to Dell asking about the depth progression went unanswered.
Other vendors' servers are deep as well, but have remained relatively consistent. The deepest 1U server from Hewlett-Packard Co. is 27.5 inches on the ProLiant DL140, DL145, DL360 and DL365 models, said John Gromala, director of server product marketing at HP.
"The ProLiant models have maintained the same depth across generations. It is more difficult to design servers within a consistent depth from generation to generation and thus has required significant innovation from HP," Gromala said. "Our two-[processor] servers have maintained a depth of 27.5 inches and our one-[processor] servers have maintained a depth of 25 inches. HP designs servers based on our customers' requirements, and depth consistency has always been a key item."
Looking at other x86 server vendors, IBM's System x3250 1U, single-socket rack server is 22 inches deep, and the IBM System x3655 2U server is 25.7 inches deep. By comparison, the 1U Sun Fire T1000 server from Sun is 18.4 inches deep, and the entry-level Sun Fire V125 server has a depth of 25 inches.
Fremont, Calif.-based Rackable Systems Inc. specializes in servers that are about half the depth of average servers. Rackable's 1U servers are 15.5 inches deep and 17.6 inches wide and can be mounted back to back, said Collette LaForce, vice president of marketing at Rackable Systems. The company also offers 1U, 2U and 3U form factors that are 28.5 inches deep for customers who want that type of configuration, she said.
"When the larger players started shipping 1U boxes, they ranged in depth from 20 inches to 24 inches on average," Goolsbee said. "This was the same or a bit longer than the average 2U and 4U boxes that preceded them, but still manageable. They could fit in two-post or four-post racks."
Conceding to this, one server vendor employee said in a blog, "[XRack Pro's] noise-reducing server rack cabinets have 32-plus-inch rail-to-rail distance, which has been plenty long in the past, but some of the new servers are starting to push the limits, and the use of a cable management 'arm' that sticks out the back of the server a couple more inches has been my biggest issue; the arm is not always mentioned up front in server marketing materials -- and/or customers don't always notice it. It can become a big 'gotcha' during install time."
The problem with growing server depth is a corresponding loss of floor space. "If your servers are now over twice as deep as they once were, entire rows of data centers have to be moved farther apart to accommodate them," Goolsbee said. "Logically, if your rows of racks are farther apart, the number of racks you can install in your data center shrinks."
When Goolsbee articulated this problem to server vendors, he said the response was that "deeper servers are not for tightly packed data centers but for smaller installations, like a couple of racks in a server closet."
"In a colocation environment like ours, when we have no control over what our customers bring in, making them buy blade servers isn't an option," Goolsbee said.Deeper servers, deeper racks
Rack manufacturers have had to re-design their products to accommodate deeper servers. Rackmount Solutions Ltd. offers 30-, 36- and 42-inch adjustable racks so customers can mount their longer servers to the first and rear set of rack rails and still have a middle set to use for rack-mount items that don't require the extra depth, said Deborah Petty, a spokesperson for Rackmount Solutions.
"It has been an increasing challenge for IT managers and their departments for several years," Petty said. "Dell has been making a 30-inch. It's a challenge more and more will face as they replace their older technologies."
Simon Griffiths, who works for a rack manufacturer, also discussed the compensation for deeper servers in a blog. "It is a constant battle for us trying to make everything deeper and deeper," he wrote.
"We have had a nightmare with Dell's quick-fit slides. They are a great time saver and a really nice design. Trouble is that they don't comply with Server System Infrastructure (SSI) guidelines, which Dell signed up for. What this means in practice is that they don't fit into some perfectly compliant racks," Griffiths wrote. "We have had to change all of our design and manufacture system for this simple thing, and even now we still get some that don't fit. . . . I have reported it to them, but . . . "
The racks used at Digital Forest are 42-inch racks from American Power Conversion Corp. Because room is needed in front of the servers for airflow and more for cabling in the rear, about a foot of buffer should surround servers in the rack. With servers running more than 30 inches deep, 42-inch racks are tight, Goolsbee said.
The 42-inch deep server cabinets add almost 2 feet to every aisle in a data center facility. Depending on the number of racks per aisle, that can add up to a lot of servers lost by having these deeper boxes, Goolsbee said.
"The ideal rack size was 18 inches; it is a perfect footprint in my opinion, but we're long past that point. Everyone wants to build 1U servers for some reason and don't give consideration to depth," Goolsbee said.
Let us know what you think about the story; email Bridget Botelho, News Writer.
Also, check out our news blog at serverspecs.blogs.techtarget.com