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I recently decided to encrypt my Xoom tablet. The process went smoothly (full power, plugged in the whole time, took about an hour) but since the encryption, it seems like my battery life has decreased. With moderate usage, I used to get close to two days worth of usage before the encryption, but now my battery usage meter has me at 15% after 23 hours.

I found this thread on the Motorola Owners' Forums but that is about it.

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Contrary to that linked thread, to me it seems intuitively that it is more work for the CPU to read files from the disk when it's encrypted than if it's not, so this is likely to use slightly more battery than otherwise. Whether that would be a noticeable amount or not I don't know. But a CPU doing slightly more work than normal means it's switching into high powered mode at times that it wouldn't have before, so will use slightly more power? –  GAThrawn Oct 4 '11 at 14:48
    
@GAThrawn I absolutely agree; more ops = more power expended. I also didn't think it would be noticeable, but it definitely is to me. I see a factory reset (the only way to un-encrypt on the Xoom) in my future. –  shambleh Oct 4 '11 at 15:18
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up vote 6 down vote accepted

Encryption is a fairly CPU intensive process, so using more battery is not unexpected. Though it depends a lot upon the apps you use and how much they read/write to the storage. I would expect that an 'idle' Xoom with encryption would last just as long as one without, but if you use an app that does lots of little writes to disk, it will end up using more CPU.

The encryption happens at the block layer. This means that small writes to the disk require a read, a decrypt, an update, and then writing the block back.

I don't see any useful stats about the actual CPU overhead. (Android is using the 'dm-crypt' module of the Linux kernel to do the disk encryption.)

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Wow, great technical page on encryption process. Thanks. –  shambleh Oct 4 '11 at 17:04
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There is a bug with encryption on the Xoom. I have been working with a Google engineer to identify the problem. Basically some of the low level kernel worker processes are not sleeping properly. If you use the full version of SystemPanel you can see which processes are prevengint your Xoom from going to sleep. Hopefully there will be a fix baked into ICS. According to Motorola it should be released in early December.

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That would be pretty wild if it is true. Thanks for the info. –  shambleh Oct 26 '11 at 12:57
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Is there a bug report that tracks this problem somewhere? –  Flow Oct 26 '11 at 14:33
    
@shambleh Is there any technical stuff (bug reports, etc.) on this? Any news? –  jon May 29 '12 at 15:14
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