Windows Server 2012 Essentials handles those scheduled nightly backups of sleeping computers quite nicely, here's how.
Wondering how long an overnight backup took? Or how it works, exactly? Dive in with me for a look under the hood, and you'll resurface with a better understanding of exactly how these backup tasks are handled.
This sort of deep dive became necessary for me to understand how things were working, ever since I began using the beta of WS2012E back in October of 2012, and bravely tried backing up 8 systems daily. In my research back then, I had discovered that there seems to be no Windows Home Server Technical Brief for Home Computer Backup and Restore for the WS2012E user. And as of May 29 2013, there still isn't!
So let's just have a look at my own Windows 8 64 bit system, a Lenovo W520 laptop, which is set to sleep after 15 minutes of no active use. It was left alone to sleep last night, and was awoken just 5 minutes after the 1am backup window began. That means it happened to be first to get backed up last night, of the 12 systems backed up nightly. How do we verify that the backup window began at 1am? By heading on over to the 'Windows Server 2012 Essentials Dashboard' and clicking on the 'Customize Computer Backup and File History' button.
Following along over in the Event Viewer, easily brought up in Windows 8 by pressing Win+X and selecting 'Event Viewer', you'll see that earlier today, this particular system woke at 1:04am, then went back to sleep at 1:34am. So it took less than 1/2 hour to perform the actia; daily overnight backup job.
The Backup Properties will show close to the time the backup was kicked off by the scheduled task. To view the 'Backup Properties' view, just double-clicking on the system entry on the Dashboard's DEVICES view, or from my client PC, the W520 laptop, I just ran:
C:\Program Files\Windows Server\Bin\BackupLaunchpad.exe
Finally, I also check out the Windows File Explorer, where I can see from the listing of files that the server laid down during that half-hour matches the expected timeline quite nicely, with the small files finishing up by 1:36am, and that last big file getting finalized 2 minutes after the laptop had already gone back to sleep.
And finally, then it finished up, it created a Task Scheduler entry for the next nightly backup, this time for 1:26am. That would seem to indicate it's sneaking in another system's daily backup before this PC, so there's some sort of round-robin approach to giving each PC a different timeslot each night. If I don't want it backup tonight, I'd just right-click and disable this entry. No worries doing that, because it'll just stay asleep all night tonight, and will automatically recreate another wake up task for the next night. Notice how it says "Last Run Time" was "Never"? That's because the scheduled task is created new, daily, and set to only run if the PC has AC power.
May 31 2013 Update:
Turns out the client PC's Task Schedule is "touched" daily, but not actually re-enabled. See how the date has changed, but it's still disabled, in the screenshot below. So I simply right-click and re-enable the task, and I'm good to go again, daily backups resume.
Here's a narrated video walk-through version of everything that's discussed in the above article.
Jun 14 2013 Update:
If you happen to sit down at your computer in the early morning and you're surprised to see it's already awake, it's quite possible the overnight backup job just finished, and your system's sleep timer hasn't kicked in yet. To verify, open a command prompt, then type 'powercfg lastwake' and here's the results you'll be looking for.
Wake History Count - 1 Wake History  Wake Source Count - 1 Wake Source  Type: Wake Timer Owner: [PROCESS] \Device\HarddiskVolume1\Windows\System32\services.exe Owner Supplied Reason: Windows will execute 'NT TASK\Microsoft\Windows\Windo ws Server\Backup' scheduled task that requested waking the computer.