Linux captures the 'green' flag, beats Windows 2008 power-saving measures

Independent tests show that Red Hat Linux pulls as much as 12% less power than Windows 2008 on identical hardware

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The active test used an e-mail test script to continuously send e-mails to the server and operating system pair under test. In the case of the two Linux distributions, we used sendmail/procmail as our SMTP server with 1,000 users. We installed Microsoft Exchange Server 2007 under Windows 2008 Enterprise Server Edition, imported the same 1,000 users, and assaulted it in the same way, by using scripts we generated. We let the operating system and application pick the number of cores to use as a default.

Summary results

With the IBM x3350, HP DL360G5, and Dell 1950 servers we performed our quiescent and active state tests twice: once with High Performance settings in place; and, the other with the Power Saver mode applied. For the HP DL-160G5 server, we could only complete the tests without the maximum power saving setting applied as the server crashed each time we attempted to toggle between the power saving settings. HP says a fix for this issue should be available by the time this test publishes.

In most cases when sitting idle, Windows Server 2008 drew slightly more power than either Linux did on the same server. The exception was when Windows Server 2008 was running in power savings mode on the Dell server, where it drew on average 3% less power.

While we've already noted that RHEL conserved more power than Windows Server 2008 in most cases, we'd be remiss if we did not also mention that RHEL drew less power than its Linux brethren in all quiescent tests. The spread for that difference was a low of .5 watts less on the IBM server when the systems were tuned for top performance to a high of over 5 watts less on the HP DL-160G5 server when the systems were in power savings mode.

During the active tests, Windows Server 2008 running in power-savings mode on the Dell box used over 7% more power than the Linux average on the same hardware. But on the IBM and HP DL-360G5 server, Windows Server 2008 pretty much ran on par with the lowest Linux consumer in those tests.

When running in the high performance mode in the active test, Windows Server 2008 used as much as 11 percent more wattage than the average Linux power draw on the same hardware. That said, Windows Server 2008 had the best power consumption rating in this test run on the HP DL-160G5 server, spending on average about 6.5 watts less than Linux.

The server hardware impact

Server makers responded to our requests to be part of the test bed with several kinds of CPU and disk configurations all housed within 1U hardware casings. Overall, the savings wasn't startling between the highest and lowest number for a server in terms of watts consumed in any test.

There's little doubt that advertised power savings numbers can be achieved, but servers will need to be tuned for both the operating system, as well as the power-savings applications' ability to control which cores are either used or put to rest in a load-balancing situation. Rather than push configurations for core optimizations (we couldn't find settings to do this for the applications tested), we let the operating systems take care of the details. The details, it turns out, was that all of the cores in all of the tests saw at least some activity both in quiescence but also in application use. SMP kernels were used for all tests.

IBM's x3350 was the leanest and greenest, both in terms of CPU 'horsepower' but also power consumed. In quiescent tests, there was less than a 2-watt difference among any of the three operating systems tested in either performance or savings mode. In the active tests, the power draws stayed within that 2-watt range with the exception of when Windows Server 2008 drew 87.8 watts, compared with SUSE's 79.6 watts and RHEL's 78.3 watts in our active test when the systems were tuned from performance.

The dual-quad core Dell 1950 sucked more power overall, but with more cores, it also delivers more computing power. In the quiescent tests, the test where settings were tuned for performance, Red Hat defied logic and used slightly more power than it did in the power savings mode, but otherwise, the results followed as logic and settings expected.

The HP DL-160 didn't show dramatic behavior changes in settings in the quiescent tests, and made Windows 2008 Server a winner in the active, performance-modes test where it seemed to give its best performance.

When we tested the DL-360G5 late in the series after having difficulties with the HP DL-160G5's Windows testing, we found it behaved similarly to the Dell 1950 (which has the same number of CPUs as this bigger HP box), consuming the highest number of watts, but also doing so with the largest number of drives.

Summary

Microsoft, Red Hat and Novell/SUSE each have power savings and green initiatives that are widely publicized. Nonetheless, we were astounded by the effort we needed to undertake in order to chase down of firmware, BIOS and other updates was necessary to get real savings in the tests we conducted. Tuning servers for optimized power savings could yield better results, but would create a new painstakingly tedious server management discipline required to constantly control the deep complexities of the configuration variables involved.

We recommend that every potentially green server deployment be thoroughly checked, as each server model may or may not have the necessary BIOS settings and operating system chipset recognition features that will result in a power savings. While all of this leg work might ring true to that famous line in the Kermit the Frog song, entitled "It Ain't Easy Bein' Green", if you consider the power savings over a five year service life, the boost to the bottom line will likely be worth the effort.

Henderson is principal researcher and Dvorak is a researcher for ExtremeLabs in Indianapolis. They can be reached at thenderson@extremelabs.com.

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Copyright © 2008 IDG Communications, Inc.

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