Online virtual machine disk migration

1. A method for migrating a virtual machine disk (VM disk) from first physical storage to second physical storage while the virtual machine (VM) is maintained in its physical location, the method comprising:

taking a snapshot of the VM disk as represented by a first parent VM disk stored on the first physical storage, whereby a first child VM disk is created;

copying the first parent VM disk to the second physical storage as a second parent VM disk;

re-parenting the first VM child disk to the second parent VM disk; and

consolidating the first child VM disk and the second parent VM disk;

wherein the VM disk on which the VM is dependent for execution is migrated from the first physical storage to the second physical storage without migrating the VM while the VM is running.

2. The method of claim 1 further comprising deleting the VM disk from the first physical storage without migrating the VM, such that the VM has remained in its physical location while the VM disk on which the VM is dependent for execution has been migrated.

3. The method of claim 1 wherein the physical storage on which the first child VM disk is created is the first physical storage or the second physical storage or another physical storage.

4. The method of claim 1 further comprising, after the first child VM disk is created:

designating the first parent VM disk as read-only; and

redirecting writes intended for the first parent VM disk to the first child VM disk.

5. The method of claim 1 further comprising, prior to consolidating:

directing a read intended for the first parent VM disk to the first child VM disk if information associated with the read is unavailable in the first parent VM disk.

6. The method of claim 1 wherein the first child VM disk is represented as a file or as a raw device mapping.

7. The method of claim 1 wherein the first parent VM disk is represented as a file or as a raw device mapping.

8. The method of claim 1 further comprising:

taking a snapshot of the first child VM disk, whereby a second child VM disk is created on physical storage;

redirecting writes intended for the first child VM disk to the second child VM disk; and

subsequent to consolidating the first child VM disk and the second parent VM disk, consolidating the second child VM disk and the second parent VM disk.

9. The method of claim 8 further comprising, prior to consolidating:

directing a read intended for the first parent VM disk to the first child VM disk if information associated with the read is unavailable in the first parent VM disk; and

directing the read to the second child VM disk if the information is unavailable in the first child VM disk.

10. The method of claim 1 further comprising migrating the virtual machine from a first host platform to a second host platform before or after the VM disk is migrated.

11. The method of claim 1 wherein said virtual machine comprises a template, wherein said first child VM disk comprises information that customizes said template.

12. A non-transitory computer-readable medium having computer-executable instructions for causing a virtualized computer system to perform a method for migrating a virtual machine disk (VM disk) from first physical storage to second physical storage while the virtual machine (VM) is maintained in its physical location, the method comprising:

taking a snapshot of the VM disk as represented by a first parent VM disk stored on the first physical storage, whereby a first child VM disk is created;

copying the first parent VM disk to the second physical storage as a second parent VM disk;

re-parenting the first VM child disk to the second parent VM disk; and

consolidating the first child VM disk and the second parent VM disk;

wherein the VM disk on which the VM is dependent for execution is migrated from the first physical storage to the second physical storage without migrating the VM while the VM is running.

13. The computer-readable medium of claim 12 wherein the method further comprises deleting the VM disk from the first physical storage without migrating the VM, such that the VM has remained in its physical location while the VM disk on which the VM is dependent for execution has been migrated.

14. The computer-readable medium of claim 12 wherein the method further comprises, after the first child VM disk is created:

designating the first parent VM disk as read-only; and

redirecting writes intended for the first parent VM disk to the first child VM disk.

15. The computer-readable medium of claim 12 wherein the method further comprises, prior to consolidating:

directing a read intended for the first parent VM disk to the first child VM disk if information associated with the read is unavailable in the first parent VM disk.

16. The computer-readable medium of claim 12 wherein the first child VM disk is represented as a file or as a raw device mapping.

17. The computer-readable medium of claim 12 wherein the first parent VM disk is represented as a file or as a raw device mapping.

18. The computer-readable medium of claim 12 wherein the method further comprises:

taking a snapshot of the first child VM disk, whereby a second child VM disk is created on physical storage;

redirecting writes intended for the first child VM disk to the second child VM disk; and

subsequent to consolidating the first child VM disk and the second parent VM disk, consolidating the second child VM disk and the second parent VM disk.