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I have a MacBook 2,16 GHz with 3 GB RAM (white from 2007) and I wonder how much free space should there be on the start volume.

I have a 100 GB partition for OS X (10.6.5) and a separate data partition of 300 GB (however the user directory is on the system partition).

free space on the start volume: 30 GB after booting 22..25 GB after one day of use goes down to about 22 GB after several days of use (I usually reboot, when it reaches 22 GB).

(there is also about 30 GB free on the data partition).

=> Could that be a performance problem or is that enough free space?

I have some large databases open in DevonThink Pro, mostly many pdf files open in Skim, Safari seems to need quite some RAM and there are some non-native apps (TexMakerX and JabRef) which also get quite slow sometimes.

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3 Answers

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According to this About.com page written by Tom Nelson:

I would say keep at least 15% of your startup drive free at all times...so that some basic OS X maintenance scripts will have sufficient free drive space to run. This includes OS X's built-in disk defragmentation system, memory swap space, and enough space to create cache and temp files when OS X starts up, while still leaving room for basic applications, such as email and web browsers, to use free space as needed.

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I've run for 3 years with no more than 10GB ever free on my 160GB disk, and quite frequently as low as 500MB free. Things seem to work just fine.

Aperture complains loudly if there's less than about 1GB free: I think that would be a sensible minimum to stick to.

Your system swap file does get recovered without a reboot -- if memory usage drops enough.

I find that Caches, particularly those of Safari.app and Spotify.app are a big cause of unnecessary disk use. You can rm -Rf ~/Library/Caches whilst the system is running without any bad effects if you're about to run out of space!

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I'd say you have enough space.

Most of the time, the decrease in hard disk space can be attributed to swap files (page files), aka virtual memory. Since the file is essentially a copy of what was in your RAM, the size of swap files are typically on the order comparable to the physical RAM size and rarely reaches like 10 times the size of your RAM (unless you have a real memory hog app).

Even if it did, quitting the hog or restarting (like you do) should free them up and is never a permanent problem.

I've never seen a case where swap files and temporary files reach 30 GB, which you have as your free space, free space should not be a problem.

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Just as a note, I've used Klix to recover photos from a 16GB SD card overnight and woke up to 40GB of swap files, so it can happen. –  daviesgeek Jul 21 '12 at 5:52
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