Backup Strategies for Integrity Virtual Machines

Volume Splitting on the VM Host
Let us now explore virtual system data protection through the VM Host. You can protect the virtual
system’s data can be protected in a similar fashion by taking the volume-splitting concept down to the
VM Host level. The major difference between this approach and splitting volumes inside the virtual
system relates to the application using that data. As illustrated in Figure 7, only one virtual disk may
correspond to a volume on the VM Host system. In order to get a consistent snapshot of the virtual
storage, one must disconnect it from the virtual machine. To do so, you may dynamically remove the
virtual disk from the virtual system – which requires transitioning the state of all applications using that
virtual disk so that I/O transactions cease. This removal flushes all I/O transactions from the
application and the virtual system out to the volume. Next, you merge the volumes, synchronizing the
physical storage devices with changes made to the volume. After the merge, split the volume again
and dynamically reconnect the corresponding virtual disk to the virtual system. Subsequently, the
application using that storage resumes execution.
Unfortunately, you cannot disconnect a virtual machine’s root disk; hence, one may not back up a
virtual machine’s operating system storage using this approach. In this case, you must shut down the
virtual machine before backing up that storage using the volume-splitting approach outlined above.
Figure 7 Volume splitting at the VM Host level. Similar to splitting in the guest, one may want to back up the “split” volume to
tape or other media after the split.