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Making a Fusion virtual disk pre-allocated or sparse (1021565)

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This article provides the steps to change a virtual disk type from sparse to pre-allocated.

A pre-allocated virtual disk is equal in size to the size assigned to the virtual machine's hard disk. So, a virtual machine assigned a 40 GB hard disk takes up 40 GB of space on your Mac (plus the space required for any snapshots, and other virtual machine files). This space is the same as the "Total size" of the hard disk shown by the guest operating system.

A sparse virtual disk is equal in size to the total used space of the virtual machine. A virtual machine assigned a 40 GB hard disk only takes up space on your Mac that is needed by the guest operating system and any programs installed in the virtual machine and any files saved there. The space used on your Mac increases as the virtual machine is used. This space is the same as the "Used size" of the hard disk shown by the guest operating system.


To change the virtual disk type to sparse or pre-allocated:

Note: Before proceeding, ensure that you have more free disk space than the size assigned to the virtual hard disk. For example, if your virtual machine has a virtual hard disk size of 40 GB, you need an additional 40 GB of free disk space to complete this operation.

  1. Shut down the virtual machine by clicking on Virtual Machine > Shut Down.
  2. Navigate to Virtual Machine > Settings.
  3. Click Hard Disk(s).
  4. Select the disk whose type you want to change.

    • In Fusion 4.x and above, this is from the drop-down menu. Then, click the triangle beside Advanced options to expand that section.
    • In Fusion 3.x and earlier, this is from the list on the left side of the Hard Disks window.

  5. Select the appropriate disk type:

    • If you want to make the disk pre-allocated, enable Pre-allocate disk space.
    • If you want to make the disk sparse, disable Pre-allocate disk space.

  6. Click Apply.

Additional Information

A pre-allocated virtual disk may give faster performance than a sparse disk. The performance return is greatest on disk-intensive activities when new sectors are being written to. This is because the sectors already exist for the pre-allocated disk, but must be created for the sparse disk. Daily activities which use the same disk sectors and files show the least, if any, increase in performance.


disk-format  disk-space  how-to  virtual-disk  virtual-disks  virtual-disk-type

See Also

Update History

08/04/2010 - Re-wrote article to make it more generic. Added background information about disk space usage and performance. 10/23/2013 - Added Fusion 6.x information. 08/21/2014 - Updated for Fusion 7.x

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