Newsletter

Do You Back Up a Running Virtual Machine?

As virtual servers and storage gain in popularity, one of the significant questions to address is data preservation. From SMB to the Fortune 500, drivers like disaster recovery, corporate policy making, regulatory compliance, and litigation support/e-discovery require due consideration to backing up virtual machines.

But the backup software has to treat the virtual machines differently from conventional physical servers. For example, there is the matter of resource use. Running multiple virtual servers on a single physical server results in better resource use during normal operations but can, in some cases, saturate those resources during backup. If you have several virtual servers running on one host, performance may suffer during the backup cycle as backup and continuing applications battle for bandwidth, unless the backup is done essentially in the background.

Backing up typically requires that the virtual machines be shut down or put into a saved state. The reason that virtual machines must be turned off or saved to be backed up by using standard file backup software is that part of the virtual machine state information is stored in memory. The state information in memory, plus the state of the virtual hard disk files, along with the state of the configuration file, makes up the current state of the virtual machine. When you back up the files for a running virtual machine, they are most likely in an inconsistent state. Backing the virtual volumes in this state can result in corrupted data in the backup copy.

Interestingly enough, though, imaging can guard high-duty-cycle users from unwanted downtime. You can take an image of a virtual machine when it's running live, just as you can image a physical server. Additionally, you can migrate an image from a physical to a virtual environment just as easily as you can migrate from virtual to a physical server.

In a VM, it's really no different. To do a simple file-based copy, you would have to shut the VM down so that the locks on those files would be released. But a snapshot and imaging capability creates a s mirror image or clone file that includes every bit on that virtual machine. Just as disk imaging software can create a live backup of a physical server, it too can create a live backup of a virtual machine without impacting user productivity or systems operations. Imaging can also be used in a tiered backup approach.