Creating RamDisk in Mac OS X

Tested with Mac OS X version 10.9 Mavericks

Steps:

1. Create an AppleScript, e.g. /Users/eddiecjc/Documents/Scripts/RamDisk.scpt

   set isTmpDiskRunning to "false"
   set isRamdiskCreated to "false"
   tell application "Finder"
    if not (exists POSIX file "/Volumes/Ramdisk") then
     -- Method 1, may have problem with system hibernate.
     -- Creating RamDisk, with size 4GB (4 * 1024 * 1024 * 2)
     do shell script "diskutil erasevolume HFS+ RamDisk `hdiutil attach -nomount ram://$((4*1024*1024*2))`"
     
     -- Method 2, using Open Source software TpmDisk.
     --do shell script "
     --  open -a /Applications/TmpDisk.app --args -name=RamDisk -size=4096
     -- "
     --set isTmpDiskRunning to "true"
    end if
    
    repeat until isRamdiskCreated = "true"
     if exists POSIX file "/Volumes/Ramdisk" then
      set isRamdiskCreated to "true"
     else
      display alert "Ramdisk is NOT created.
   Retry in 5 seconds..." as critical buttons {"I will wait"} giving up after 5
     end if
    end repeat
   end tell
   
   -- Create Folders
   set FolderPath to POSIX file "/Volumes/Ramdisk" as alias
   tell application "Finder"
    try
     make new folder at FolderPath with properties {name:"Library Caches"}
     make new folder at FolderPath with properties {name:"Downloads"}
     make new folder at FolderPath with properties {name:"Temp"}
     make new folder at (POSIX file "/Volumes/Ramdisk/Temp" as alias) with properties {name:"Screenshots"}
     
     -- Set up symbolic link
     --sudo rm -r ~/Library/Caches
     --ln -s /Volumes/RamDisk/Library\ Caches ~/Library/Caches
     --sudo rm -r ~/Downloads
     --ln -s /Volumes/RamDisk/Downloads ~/Downloads
     
     -- Change screenshots default location
     -- defaults write com.apple.screencapture location /Volumes/Ramdisk/Temp/Screenshots
     -- killall SystemUIServer
    end try
   end tell
   
   if isTmpDiskRunning = "true" then
    -- Kill the process, so it does not take up the space from the task bar.
    set app_name to "TmpDisk"
    do shell script "killall " & app_name
   end if
   
   -- 1. Export this to type Application RamDisk.app.
   -- 2. Mark as Run-Only
   -- 3. Mark the file as executable with chmod +x .
   -- 4. Add RamDisk.app to Login Items in the Users & Groups. 
   

2. Export the script to type Application, e.g. /Users/eddiecjc/Documents/Scripts/RamDisk.app, and mark it as Run-Only
3. In Terminal, mark the file as executable, e.g. chmod +x /Users/eddiecjc/Documents/Scripts/RamDisk.app
4. Add the script to run during start up
   1. Open System Preferences
   2. Go to Users & Groups
   3. Select the current user
   4. Go to Login Items tab
   5. Click on "+" and navigate to the RamDisk.app
   6. Repeat for other users that would need a RamDisk
      
5. Run RamDisk.app to set up the RamDisk as a preparation for the remaining steps.
6. Move stuff to Ramdisk:
   • Move ~/Library/Caches to Ramdisk

     sudo rm -r ~/Library/Caches
     ln -s /Volumes/RamDisk/Library\ Caches ~/Library/Caches
     

   • Move Downloads to Ramdisk

     sudo rm -r ~/Downloads
     ln -s /Volumes/RamDisk/Downloads ~/Downloads

   • Move screenshot default saving location to Ramdisk

     defaults write com.apple.screencapture location /Volumes/Ramdisk/Temp/Screenshots
     killall SystemUIServer

     Reference: http://simonemccallum.com/2013/08/11/how-to-change-the-default-location-for-your-mac-os-x-screenshots/
   • Change any default download location for apps (e.g. Chrome)
   • Change the unarchiver default working directory.
7. If using the built-in command rather than TmpDisk, for laptops, change the hibernation mode, to prevent Ramdisk being ejected after hibernation.
1. Find out the current hibernation mode:

   pmset -g | grep hibernatemode

   Default is 3 for laptops, indicating contents in the Ram will be written to the hard drive before going to hibernate mode.
2. Change it to 0, so battery will still power the Ram (drawback is that if the battery is drained or power is lost, then resuming from hibernation would fail):

   sudo pmset -a hibernatemode 0

3. Clean the disk space used previously for the hibernation:

   cd /var/vm
   sudo rm sleepimage

   Reference: http://blog.roodo.com/jason1204/archives/25384258.html and http://etherealmind.com/osx-hibernate-mode/
8. Restart the Mac, Ramdisk should be created after log in.

Note: Mac OS X comes with built-in command to create virtual disks using ram, as described above, but there is a problem of Ramdisk disappearing after the hibernation. To get around this issue, there is an Open Source ramdisk tool called TmpDisk, download and install TmpDisk from http://inkscribbles.com/apps/tmpdisk/. Comment out method 1 in the script and uncomment to use method 2 instead.