Why Don't Servers Support Power Management?

Cerlyn asks: "I am the network administrator of three server grade machines purchased from three separate companies. The recent power problems in California reminded me of the fact that none of these servers seem to support power management. The operating systems these systems run (Linux 2.2, 2.4, and FreeBSD 4.2) are compiled to support power management, but do not detect any power management capabilities at all. Granted, no one wants a server sleeping on the job. But the way things seem to be coded, processors can not even sleep while idle without known hardware support. Lightly loaded machines are often idle 75% of the time or more. Sleeping while idle could make them save a significant amount of power. For many companies, the extra ten seconds it would take to spin up a backup server's hard drive(s) likely would be a non-issue. So, why don't server grade computers support advanced power management (APM), APCI and the like?" And in the land of the rolling blackout, one has to wonder if the potential power saved could help the situation, assuming a good percentage of the big iron in Silicon Valley were configured to conserve what power it could (as opposed to adding on to the drain as it is now).

Comments

Re:It wont save any power ...

[rnturn]

``drive spinup seems to be the time when a borderline drive will fail''

Not to mention that it's the time when the drive's current requirements are the greatest. These inrush spikes are not a big problem for a system with a drive or two but I've seen places with systems with large RAID arrays attached to servers where they popped breakers if the power came back on while the drive cabinets were sitting there with their power switches in the ON position. Apparently, not all setups allow you to or are configured to use the SCSI start command to sequence the drive's startups like they used to do in the days of yore. Happily, newer drives are not as power hungry (I can remember some old 5.25 inch disks that used 40+W of power) but now that these 15,000 RPM drives are coming out...

If you're trying to save power turning off the monitors when no one's actually sitting in front of them helps enormously. Where I used to work, whenever there was a power outage and we switched over to the UPS (no generator while I was there) standard procedure was to immediately turn off any monitors that no one was actively working on. Gave us well over another half hour or more of battery time. Switching to KVM boxes to handle, say, eight servers with a single monitor halped out a lot too.

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A few bits of info

[arivanov]

First, I agree power management in a server makes sense. But not because of california legislations but because the most important server parameter is MTBF. Power management can increase the MTBF and efficiency of the cooling subsystem. This in turn increases MTBF of disks and the entire system. One degree away from the optimum operating temperature can decrease a disk's life by an year or more.

Also, you do not spin down disks on servers for both business and reliability reasons. The business reason is server latency. The reliability reason is that most server HDUs hate to be spun down and their MTBF decreases (which is again business in a sense). Also, the biggest power eaters in most modern servers are the cooling systems and the CPUs. Not the disks. Disks hardly go above 2-10W nowdays while a PIII with the fans can go up to a 100W. Alpha goes even beyond that. Also, spinning up and down disks to 7200-10000 RPM can actually generate more heat and consume more power than keeping them running.

Some bits of info by platform:

• x86APM does not work at all or has only limited functionality with SMP systems and any newer boards. Which means that only an ACPI supporting system will have working power management. ACPI is a new addition in linux and BSD. Neither ACPI nor APM exist in solaris. NT is not really using it for power management in servers to the extent of my knowledge. So only a very upto date installation can actually use power management. But it will be only the CPUs. I have yet to see an x86 server where the fan is actively controlled by chassis temperature. Usually servers have them hardwired at MAX. Which means the entire exercise meaningless as you are not actually improving your MTBF that much.
• Alpha Only recently someone (forgot who) modified the original DGUX PAL code to do power management on the newer CPUs. This is hardly used and unusable in all AlphaBios installs. Which is a pity as the alphas have always had the fan speed controlled by CPU temperature.
• MIPS - never heard of power management. Server lines of PPC derived (u)Sparc - same.

So overall the situation is that for one of the most popular platforms the power magement is hardly used due to the fact that the OS support just came in. For the second most popular platform (Sun) the power management was never there. The others are pretty much there as well.

And to conclude: I do not feel comfortable installing linux 2.4.0 or the ACPI support for BSD on real production machines yet.

Why should a server save power?

[funkman]

There not meant to. If a server is in a position where it can go into a power saving mode, then someone has not done a good job on the server farm. Consolidate any boxes that have that light of load so light that they may frequently go to sleep. With consilidation: you save on administration (less boxes) and you should be more secure since there are less boxes to administer AND you'd be saving power because you are using less boxes.

But lets say you need a box that needs to be on its own and has the ability(time) to spin down. I personally would not want this not because of the extra time for the spin up, but because the spin up is hard work on a motor and for a server - once that hard drive is spinning - keep it spinning. There is much less wear on the motor to keep it spinning than spinn up process. This should give a more predictable life to the drive.

Power Saving Matters

[Alan Cox]

Compiling in power management support on the test boxes I use cut the power bill by 20%. A lot of that actually seems to come from monitor powerdown rather than CPU idling, but with an Athlon drawing 60 watts of power at peak (or 240W once we all have nice quad athlon boxes) its still a substantial saving.

For most boxes the cpu halting BSD and Linux do will actually give almost as good results as the APM bios. On laptops APM bios is often measurably better as it is able to reconfigure SDRAM timings and the like in ways only practical for box specific code.

Incredible DOS Attack on California Power Grid

[lildogie]

SACRAMENTO - The California power grid was taken down today by a so-called "packet storm," where script kiddies coordinated themselves to ping every sleeping server in California to wake it up ...

Re:Spinning down any HDD is a bad idea.

[zensonic]

There are too many things that can go wrong when drives spin up and down. Particularily if the drive hasn't been idle for a large period of time.

I have had disks which have spun for years without problems in a server, but when taken down
in order to upgrade the machine in some way. Some disks don't survive. Why you might ask? The above post is one point. Another is that the heat of old drives really degenerate the components of the HDD and thus it can't stand the powerup cycle which normally puts more stress on the components.

Other HDD have used all the lubricant inside during the years, and when powered up after a server upgrade the HDD doesn't have the power to compensate for the not so smooth motion anymore.

If it ain't broken don't stop it :)