Power off or sleep at night?

I have always simply left my computers on at night, not bothering to power them down since the power management on my machines usually kicked in and turned off the displays. Having spent so many years on the Windows platform with machines that took a tremendously long time to boot up I was simply used to leaving machines on all of the time.  As a software developer—and one that for the last 10 years has created web server applications—I have adopted an always on, server kind of mentality.

There was that accessibility factor—I wanted my machines to be there when I need them, available the second I walk up while I have someone on the phone asking me a question that can only be answered online. Not "Hold on while I pull this up..." and then sitting there for a couple of minutes while the machine fired up. Having built and maintained online service businesses in the past I always needed instant access in the event there was a problem with our servers.

My switch to Mac changed that to a large degree. Macs go to sleep nearly instantly and wake up just as fast. Other than the network connection re-synching—which takes a few seconds—the machine is ready to go.

Energy costs and conservation are dominating the news lately so I also became curious about the impact of leaving my machine on all night long. Was it drawing that much energy? How much did that cost?

With the recent acquisition of an APC UPS I now had some additional data available to me via the LCD on the front of the unit. Among other things was how much power is actually being drawn through the unit, giving a pretty good picture of my Mac Pro's overall energy footprint.

I grabbed our most recent power bill to look up my rates. The most expensive months for power in my area are June through September when people are running their air conditioners full time. The rate is $0.0747 per kWh, compared with a $0.0590 per kWh rate for the remainder of the year.

Some Interesting Data
With all of the information available on the LCD display of the APC unit I tried viewing the power draw from the Mac Pro, both at near idle and under reasonable load. Keeping in mind that my Mac Pro is the latest generation version with dual quad-core 2.8GHz processors, 3 internal hard drives and two 20" LCDs attached, here's what I found:

 Watts UsedBattery LoadTime on Battery
On and Idle 20723%22 minutes
Medium CPU Usage, HD activity 28032%16 minutes
Idle, Monitors Off15017%31 minutes
Sleep Mode00%785 minutes

In sleep mode the Mac Pro draws so little power it didn't even register on the APC. 

Since normally I was leaving my machine in Idle mode with the monitors auto-sleeping I was burning 150W for the 6-7 hours I slept at night. Yes, I know, I'm on the computer a bit too much. Realistically I am completely away from my machine and not requiring it to be active for about 12 hours a day. So what does that translate into?

12 X .150kW = 1.8kWh * $0.0747 = $0.13 per day or $4.09 per month during the summer.

For me, from a purely economic standpoint, the $4 per month in savings is not all that much. A value meal at Taco Bell? A gallon of gasoline (soon to be half a gallon)? What does bother me is the environmental impact of having the machine on and at full power all the time. It seems as wasteful as keeping a couple of 75W light bulbs burning on throughout the night in case I might need some light.

Though OS X has some great power scheduling options I've found that my erratic work hours doesn't lend itself to a schedule so now I'm just getting into the habit of letting my Macs sleep when I'm not in front of them.


Josso said…
If you have a lot of programs open (Mail.app, Safari, TextMate, Adium, iChat, Spaces, 5xFinder, iTunes, Quicksilver and maybe a few more)
How fast is it to go to sleep, and awake?

How fast is it normally?

You know... I'm going to buy a Macbook Pro. ;)

Greetings from the 15 year old boy from Denmark,
- Johan
Anonymous said…
Hi Josso.
It's Pretty fast. I'd say more or less the time it takes to reconnect to the wifi + 2 or 3 seconds in my case (1. gen macbook running 10.5.2).

I'm in ur interwebz, answering ur questionz. ;-)
Mike D. said…
@josso I usually have flock, stickies, miro, adium, and occasionally iTunes open, and waking my MPB from sleep has not caused me any frustration. I haven't timed it, but I haven't been annoyed with it either. MBP's are the the best all around laptop available.

@David Alison I'm impressed that you mentioned some good reasons to put computers to sleep when they are not used...even more important if your electricity is coal fired.
Anonymous said…
I used to work for a very large media company (I'm not going to name it) and when we made the switch from OS 9 to OS X, they hired a former Apple employee to give us training on the new OS.
One of the things the trainer said was that they used to test the life of their computers by continually shutting them off and powering them back on. She recommended putting them to sleep over night, not shutting them down, and only powering them off over the weekend.
I have a Powerbook, and though it's only a couple of years old, I rarely shut it down. Still works great for me.
Unknown said…
Mr Alison, I notice the cost of electricity is quite low, may I know which part of the US are you residing. My apologies for being off topic. I am paying $0.16 per kWh.Thanks
Mike D. said…
@anonymous...or anyone else;)

what would be the problem with shutting down abd rebooting, aside relogging into everything.
Anonymous said…
The best thing to do is Log Out, then sleep. Logging out will help clear out data left over memory or apps running in the background that could possibly get corrupted. I did a non scientific experiment with my MBP. For a month I did just sleep. Left mall my apps running. After awhile I would have some apps act a bit goofy ( MS apps ). Next log out and sleep. Never had problems at all doing that. Plus starting up is really quick. Instant on, enter password and your good to go in a few seconds.
David Alison said…
@PK: I am in Virginia, just outside of Washington, DC.
David Alison said…
@Anon: I disagree on that one - logging out defeats the advantage of immediately regaining access to key applications. While I do logout/reboot my machines on occasion it's rarely more than once a week or two. Some applications do leak memory over time; the biggest culprit for me has actually been the Gmail Notifier from Google.
Anonymous said…

I find the sleep function with MAC so much better then hibernation within Windows. It seems to have fewer issues. Running hibernation within Windows I have encountered problem with some applications giving me general application faults when coming out of hibernation. I went from five Windows PC to a Dell Laptop and VMware Serve to a MAC Book Pro and VMWare Fusion.

I have read the Fusion 2.0 will be a free upgrade for current users. I am also not far from you I live down in Lorton, Va getting ready to move to Ashburn.

P.S. I enjoy reading your blog.
eric said…
BSD unix and thus OS X have several built in maintanence routines which by default are scheduled to run nightly between 2AM and 5AM. There are additional routines designed to run weekly and monthly. If you shut down your machine (and I assume if its asleep also) then you'll need to run those routines manually or use something like Macjanitor: http://personalpages.tds.net/~brian_hill/macjanitor.html.
Anonymous said…
"If you shut down your machine (and I assume if its asleep also) then you'll need to run those routines manually…"


"However, the situation isn’t as dire as you might think. First, if you put your Mac to sleep at night, instead of shutting it down, Leopard is smart enough to run the missed scripts the next time you wake up your computer. […] Second, the tasks these scripts perform aren’t so important that a few missed executions will adversely affect your Mac."
David Alison said…
@Eric: Anon has it right; when you wake your machine in the morning any of the maintenance routines that would have normally run during that sleeping period are automatically executed. I covered that in this post a couple of weeks ago.
Shearn said…
One of the reasons I don't put my computer to sleep is that I've heard that it's not good to have your hard drive spin down/spin up. It will last longer if you keep it spinning all the time. The same goes with the display. It's more stressful for your display to turn off/turn on regularly. Are any of these arguments still valid?
David Alison said…
@Shearn: There many debates on this issue but little hard data that I can find. The closest has to do with hard drive failure rates from Google (it's a PDF). Scanning through that report I believe that newer model drives have such a high MTBF rating that powering them up and down has little significance.

Does the initial spinning up of the drive platter create a shock to the drive that wears it down? Probably. But it is still a moving part and the constant spinning also creates wear and tear.

Given this I am going with the information I do know: that my drives spinning while they are not needed are burning energy that can be conserved. That much I am sure of.

On the display front—especially for LCD displays—there is no question that turning it off or letting it go into low power mode will extend its life AND save power.
Anonymous said…
"On the display front—especially for LCD displays—there is no question that turning it off or letting it go into low power mode will extend its life AND save power."

Yes current LCDs use fluorescent tubes that will have a much longer life if dimmed or left to shut off. Fluors also have a shorter life span if frequently turned on and off but a twice or three times a day cycling should actually result in longer life.

"The closest has to do with hard drive failure rates from Google (it's a PDF)."

The real conclusion of that report was size and brand have little to do with failure rate despite many people saying "I will not ever buy "X" brand again. All hard drives suck and the only reasonable cure is to be meticuously backed up. Having said that, I think we turned a reliability corner with the 120-250GB drives, though mtbf is just that - some drives still fail after only a few hours.

Lastly, why not give that big MacPro something to do overnight? You have massive computer power yet do not render either video or 3D. Fire up a copy of Final Cut, Shake or Modo and get a new hobby.
David Alison said…
@Anon: Man, the LAST thing I need right now is another hobby. I've done some basic video work on the Mac Pro using iMovie and iDVD, tasks the Mac Pro screamed through compared to the little MacBook I have.

My problem with video is it's just so time consuming from a creative standpoint. I've lost many hours of my life to perfecting scenes and transitions, blissfully ignorant of the passage of time until I tried showing the results to my family. 10 minutes later: "Oh, that's really cool". Me: "But that took 3 hours to do!".
Anonymous said…
Just in case for those who've missed it so far: Apple has not exposed this to the user interface, but the newer Macs can in fact use different kinds of sleep, similar to Windows and Linux — just more reliably. ;-)

While there is a way to switch between "sleep" and "hibernation" via command line, there is also the handy SmartSleep utility which is exactly what Apple should have provided all along.

Basically, if immediate sleep (with immediate harddisk spindown!) is desired, just use "sleep". If the battery goes flat or you lose (UPS) power otherwise, your session is lost, however.

Apple delivers all portables set to "sleep & hibernate" which lets it sleep and wake immediately, but the RAM content is saved to disk on every sleep to buffer any unexpected power loss. Moving the MacBook around during the sometimes extensive period of saving the RAM can cause damage to the harddisk, so on the road I usually prefer simple "sleep" instead.

Since I use my MacBook Pro somewhat intermittently, I usually let it "hibernate", which means it will save RAM contents to disk and then shut off completely without drawing power from the battery at all. Waking up requires a push of the power button, though, and several seconds for re-loading the previous RAM contents back from disk.

My older PowerMac G5 doesn't support that feature, apparently, or I would use it there as well for extended periods of non-use. But as far as I know newer non-portable Macs do support it by now.

The SmartSleep utility can also switch between "sleep" and "hibernate" automatically depending on the battery capacity remaining. Very nice!
Anonymous said…
I prefer putting my Mac to sleep rather than powering down because I like to preserve my working state. I usually only power down my mac on when applying some system update that requires a reboot.

One thing to remember about Mac OS X. It is Unix underneath the covers and Unix prefers to keep running. By default, Unix runs its periodic system maintenance in the middle of the night. Apple has not chosen to alter the schedule for this for a reason I cannot fathom.

So, I manually modify the schedule for the /etc/periodic scripts to run during the day (during my lunch hour). I then let my machines sleep all night. However modifying these files [either /System/Library/LaunchDaemons/com.apple.periodic* on 10.4 and 10.5, or /etc/crontab on earlier versions] requires administrator privileges and a bit of Unix knowledge.

As an alternative, you can use the sleep/wake scheduling in the Energy Saver System Preferences to wake up at 3am and go back to sleep at 4am, allowing the periodic scripts to run.
David Alison said…
@Anon: As Ping points out above, if you put your machine to sleep at night any of the maintenance scripts that should have run during that period execute when you pull it out of sleep mode. There's a really detailed article from MacWorld on this that Hendrick pointed out to me a while back:

Set newer portable Macs' sleep mode
Anonymous said…
I agree 200% on the power saving position.
150W all nights long may not cost a lot of money, but multiplied by the number of computers on earth, it is an unbelivably high and easy-to-avoid loss of energy (and therefore pollution).
The 10 seconds advantage is really not worse this waste.

In the "usefull shortcuts" serie, there are keystrokes for rebooting, going to sleep and shutting down :

ctrl-cmd-eject -> reboot (proper reboot)
ctlr-alt-cmd-eject -> power off
cmd-alt-eject -> sleep
Anonymous said…
Just to add to the key combinations:

shift-ctrl-eject -> sleep display(s)
David Alison said…
@Popey: You bring up an outstanding point that I failed to mention. The aggregate power consumption from machines left on all night long is huge. Thanks man.
Anonymous said…
Ping : I didn't know this one ! Great :-)
cwick said…
ive got a g4 quicksilver with 2 hds, & i almost always just put it to sleep at night. i find thugh that after 3 or 4 days i almost always have to do a restart cuz apps start to act a little goofy and it starts to get a bit sluggish...

i think i may try logging out, then sleep, and c if that helps so i dont have to restar every 3 or 4 dys...

love the blog btw....thanx

lottadot said…
Another good key combo, especially for the macbook/pro's - powerkey-s. It puts it to sleep quite nicely, and it's very difficult not to remember that key sequence.
Pecos Bill said…
I only shut my computers down when I'm going on vacation. IIRC, my setup uses about 250w (on, idle) but I have a 24"WS and a 19". I didn't think to check my usage with the displays sleeping. I think your 8-way uses less power than my 4-way. I have 2G on otherwise stock. Can't even recall what speed procs (midrange on 1st Gen). The setup uses ~8w when sleeping. I found that my 2 speakers/subwoofer use 40w so I have them on a powerstrip. Oh, I never log out either. It works beautifully.

Also, if I know I'm going to be away for quite a while, I will manually sleep them too. I have the front power button on my Mac Pro set to sleep it so I use that or cmd-opt-eject. I also use a freeware utility to use WOMP to wake my G4 server and put it back to sleep. (search WOMP at macupdate.com). It uses Applescript and ssh to put the remote computer to sleep.

The maint. scripts don't always run with Tiger. Leo fixed that. (I had problems on my MacPro/Tiger that were fixed with the maint scripts. No clue what it was.

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