Sleeping SAN for an energy-conscious world

Running at a lower rate 60% of the time drops SAN-related power costs by roughly 40%

US Navy servicemen and women don their blues, whites or khakis, depending on the occasion and task at hand. For systems engineers at the Navy's Surface Combat Systems Center, however, the color of choice these days is green.

"With storage, the entire world has long dealt with performance and availability. Now we're adding in a green component," says Les Martin, a civilian tactical systems engineer at the SCSC. For the SCSC, that means automatically powering down -- but not turning off -- drives when they're not in use. This giant "sleeping SAN," as he calls it, potentially could reduce the SCSC's annual power costs by 40%, he says.

For this storage-area network (SAN), which houses 168TB of data, SCSC uses the Xiotech Magnitude 3D 3000 Series Fibre Channel system. Energy-efficient 750GB Serial Advanced Technology Attachment (SATA) drives, made by Seagate Technology, fill the chassis.

The SAN's drives each consume 12 watts per hour during normal read/write mode. This compares to the 13W per hour required by the smaller 500GB SATA drives typically used by industry at the time of the Navy's procurement, Martin says.

"That might not seem like much at first read, but we are able to achieve a 7.75% automatic energy reduction in normal read/write consumption while achieving a 50% increase in storage space in a seamless and highly virtualized system," he adds.

For reasons of national security, Martin says, the SCSC must not completely power down the idle SAN drives as some enterprise IT organizations might do. A 750GB drive consumes 0.8W of power when in sleep state, but can be powered up again in about four seconds. That's roughly equivalent to the amount of time a screen image takes to materialize once a cell phone is flipped open, he notes.

"We use the minimal amount of consumption we can without hindering the users in any way," Martin says. "We had to make this fit our culture." This effort earns the SCSC a 2007 Enterprise All-Star Award.

Based on SCSC metrics on how and when analysts access data, Martin expects the SAN, which comprises more than 200 drives, to run in sleep mode roughly 60% of the year. Even without powering down completely, the anticipated energy savings are significant, he says.

Collectively, based on the 12W-per-hour consumption rate, SCSC's SAN drives use 3.1kW of power per hour when not in sleep state. In that scenario, power costs tally to US$6.96 per day, or US$2,544 annually. This compares to 2.4kW consumed per hour when all drives are asleep. Running at that lower rate 60% of the time drops SAN-related power costs by roughly 40%, to US$2.78 per day or US$1,108 annually, Martin says.

To help the industry better understand energy-efficiency efforts, Martin expects to share his SAN power consumption findings with the Storage Networking Industry Association's Green Storage Council. "We hope to be able to report the actual measured savings, say a year's time of use, to show the efficacy of a sleeping system," he says. After all, he adds, "if you're not measuring, you're only guessing."

While the industry tracks the energy efficiency of sleeping SANs, the US Department of Defense is keeping close tabs on the infrastructure in general. The SCSC is the first of its kind to move data electronically from shipboard computer programs to far-flung labs for analysis.

Traditionally, data was stored on recordable media, which then was transported manually from site to site. As it automates this process, through what it calls the Tactical Load Management System (TLMS), the Defense Department has to be absolutely certain that data is not modified as it moves across the network. The concern is the computer programs then would require recertification for use on the shipboard systems, Martin says.

As part of the TLMS, Crossroad Systems' storage routers direct data onto the storage infrastructure. Using Xiotech's TimeScale replication appliance, copies of the data can then be sent to one or many data-analysis labs.

"Labs used to have to wait for the sneakernet and the data to arrive, literally, in a van," says Martin, adding that this could take 12 to 17 days. "Now we have the ability to deliver in near-real time, depending on the robustness of the IP pipe, a copy of that data at a geographically distant and remote [Defense Department] analysis lab. We're nearly eliminating the negative costs of the sneakernet and the ever-escalating high costs of a human touching the data."

The TLMS, in place at four sites, will become fully operational in early 2008. An additional 12 sites will follow in a second phase called "SANs across America." As these come on board, the sneakernet can be disassembled, Martin says.

The SCSC implemented the power-managed storage architecture for approximately US$725,000. Over the next year, it expects to see a $1.5 million ROI in support of the four most modern shipboard computer systems, Martin says. Updates for these are delivered to SCSC quarterly, at a cost of US$150,000. Plus, Martin estimates he'll be able to trim about US$4.5 million out of the budget by eliminating the cost of gas, salaries and other expenditures associated with the sneakernet.

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