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OS X - Operating System General OS operation information and support

Time (and space) Machine


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waitomo

 
Member Since: Jan 16, 2010
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I just completed a backup to my external drive using Time Machine.

Just to experiment, a minute after it finished, I created a 20 KB Word document containing exactly one letter (a lower case "j" to be exact).

I told Time Machine to do its thing again and (not to my surprise) it told me it was backing up 13.3MB. By my math, that's about 665x the size of the minor change that actually took place on my machine.

As I've found some somewhat technical explanations that I can't quite grasp, can someone here explain in simple terms why this happens? Because it seems to me Time Machine is just sucking up space on my external drive.
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MYmacROX

 
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When you tell Time Machine to "do its thing", it does more than backup that one single file that changed. It takes a "snapshot" of your whole system as a restore point. It isn't a literal "copy" of ALL your files, settings, etc. Just a reference point to go back to if you so desire. That's why the size of the backup is larger than that single file and not as large as your entire HDD's contents.

That's my best understanding of T.M. Someone can correct me if I'm wrong...

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chas_m

 
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Because when you created your 20K word file, you also altered the logs for Word, the system, used temp space and did a hundred other things not known to you in the background.

Things change CONSTANTLY when a Mac is in use. LOTS of files are "touched" in the process of doing almost any operation. Since all those files now have a slightly different modification date than the last "snapshot," TM is obligated to back up *all changed files,* not just the new one you created.
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waitomo

 
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Thanks for the simpler answers. Appreciated. I now (sort of) understand. Which is better a place than where I started.
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MYmacROX

 
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The great thing about T.M. is even if your external eventually fills up, the newest backup will simply delete the oldest. So it will always continue to create new backups.

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