Fusion automatically sets hard disk buffering according to what guest operating system you use, but you can change the setting.

Hard disk buffering can increase performance of your virtual machine. Hard disk buffering can also consume more memory on your Mac host than operating unbuffered. Fusion enables or disables hard disk buffering based on your virtual machine's operating system.

For all Windows Vista and later guest operating systems, Fusion defaults to unbuffered I/O for Mac hosts. The same is true for all Windows 2000, 2003, XP, and XP 64-bit guests newly created with this version of Fusion. All other guests default to buffered I/O on Mac hosts.

If you are not familiar with the options, keep the default setting.


  1. Select Window > Virtual Machine Library.
  2. Select a virtual machine in the Virtual Machine Library window and click Settings.
  3. Under Other in the Settings window, click Advanced.
  4. Select an option from the Hard disk buffering menu.
    Option Description
    Automatic Fusion determines your operating system and enables or disables hard disk buffering depending on which type of buffering provides the best performance.
    Enabled The virtual machine's operating system uses buffered I/O.
    Disabled The virtual machine's operating system uses unbuffered I/O.