You can simply use command to create a ramdisk.

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diskutil erasevolume HFS+ "ramdisk" `hdiutil attach -nomount ram://512000`

This is 250 MB ramdisk, you can change 512000 to change the volume of the ramdisk.

If you want to use ramdisk for your safari cache

You can close the safari and run these

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rm -rf ~/Library/Caches/com.apple.Safari
mkdir /Volumes/ramdisk/com.apple.Safari
ln -s /Volumes/ramdisk/com.apple.Safari/ ~/Library/Caches/com.apple.Safari

Another app’s caches you can just modify path form the code above.

If you need it runs automatically when you reboot.

You need to make a file called rc.local in your /etc/
Use text editor create a file called rc.local and drop to /etc/ and confirm the password.

The code should be like this (for Safari and Chrome cache, Firefox is easier, just search from Google)

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#!/bin/sh
if [ ! -d "/Volumes/ramdisk" ]; then
	diskutil erasevolume HFS+ "ramdisk" `hdiutil attach -nomount ram://512000`
fi
if [ ! -d "/Volumes/ramdisk/com.apple.Safari" ]; then
	rm -rf ~/Library/Caches/com.apple.Safari
	mkdir /Volumes/ramdisk/com.apple.Safari
	ln -s /Volumes/ramdisk/com.apple.Safari/ ~/Library/Caches/com.apple.Safari
fi
if [ ! -d "/Volumes/ramdisk/Google" ]; then
	rm -rf ~/Library/Caches/Google
	mkdir /Volumes/ramdisk/Google
	ln -s /Volumes/ramdisk/Google/ ~/Library/Caches/Google
fi
 
if [ -d "/Volumes/ramdisk/com.apple.Safari" ] && [ -d "/Volumes/ramdisk/Google" ]; then
	echo "Ramdisk is enabled!"
else
	echo "Error"
fi

You can also modify this if you need.

More information

Testing software: Blackmagic Disk Speed Test

10 Bit YUV 4:2:2 PAL Default SSD Default Ramdisk
Disk Write Speed MB/s 180 800
Disk Read Speed MB/s 210 800

4 Responses to “How to Use Ramdisk in Your Mac”

  1. I followed your instructions and created a file called rc.local with the above script. Ramdisk is not created upon reboot in 10.8 for me, however.

    • In my case it worked good on my 10.8.2 mac air.
      You might not have privilege to edit the rc.local file.
      Try to use sudo vi or sudo open -a TextEdit /etc/rc.local
      Also make sure the rc.local file is executable. Use command sudo chmod +x /etc/rc.local

  2. rc.local didn’t work for me. I put the script in to my startup objects. works fine!

  3. doesn’t work on my macmini 2.3ghz core i7 4GB 1600Mhz os X 10.8.2

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