Energy efficiency - turning off vs leaving idle

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Energy efficiency - turning off vs leaving idle

Postby john_h » 2006-01-23 13:26

This report on energy wasted through appliances being on "standby" makes me wonder what is the best approach to energy efficiency with a desktop PC.

At home we have a typical desktop PC, CRT monitor, running Debian. When the PC is going to be unattended for more than an hour or so we'll typically turn it off, and certainly turn it off overnight.

But given the energy required to boot the system up, would it be more efficient overall just to log out, put the monitor on standby but otherwise leave the PC switched on? Would it make any difference to drop the runlevel down to single-user mode while the PC is unattended (not a security risk as you need to enter the root password to enter single-user mode proper, or hit Ctrl+D to return to runlevel 2)?

In short, how long, approximately, does a typical desktop PC have to be turned off before the energy saved in turning it off outweighs the energy consumed in booting up?

I know this is a forum devoted to Debian, home of the 723-day uptimes, where rebooting is for wimps, etc ;), but wondered whether anyone had any thoughts on this issue as it applies to a desktop system.
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Postby Jeroen » 2006-01-23 18:30

I think the enery difference of a *desktop* system doesn't differ very much from idle to busy. Unless you do such things as suspend/severely slow down the CPU, suspend the harddisk, and stop the system fans, I think (but that's a guess) that if system bootup takes 2 minutes, it's already efficient to turn the system off for 3 minutes and having it boot during 2 more minutes if you don't need it for 5 minutes.

For laptop's this is different, because in proper standby/sleep/whatever mode, they actually consume only very little power -- just enough to keep the power button working (but that works even when powered off), and to keep the data in RAM that's there.

The tricky part for a desktop system is getting the harddisk to shut down, because Linux will nearly always continuously try to write stuff to your harddisk. Of course you can stop that, but it takes a lot of tweaking, as this is not a condideration typically while developing programs and such.

But who am I to say such things with my 59 days of uptime for my desktop system and 217 days for my server (forums.debian.net, actually)...
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Postby kink » 2006-01-23 21:26

I'm saving a lot of energy with wake-on-lan. I used to keep my system running because I wanted to access it remotely. Now when I leave I just shut it down, and wake it up whenever I need it.
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Postby gabriel » 2006-01-23 22:00

I've heard opinions (of more experienced people) that "sleep mode" isn't really secure and it's better to don't do it.

I've noticed, that MS advices to not turn off future vista machines - so that they'd boot in second from a sleep mode (which saves energy etc).
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Postby Jeroen » 2006-01-24 00:34

Sleep mode isn't per se insecure -- it can just be that (a) it's buggy and your system fails to wake up from sleep, or (b) it doesn't actually sleep deep enough and still eat energy some way. Both are (unfortunately) still quite common issues with linux on laptop's. If it works, it doesn't really hurt to do it.

It is not insecure from a breakin or whatever perspective, at best your system is totally unreacheable from remote and from local processes -- because the system is effectively halted, at worst, it is as if your system was just running normally, in which situation I'd hope your system isn't insecure either, or you lose anyway.
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Postby jjmac » 2006-01-29 10:48

As for turning things off and bootups, i think the main issue with company sites and the like has to do with disk ware. As in, most of the friction based ware will occure when the mechanism is cold.

As for suspend states ... something i need to find out about more.

Overnight shutdown for a personal box --- of course, but just for an hours unattention, better just configuring X to shut the drives down after a while and suspend the monitor.


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