Backing up servers has never been easy, but at least in the past you could say that the process was trivial. These days though, with the introduction of virtualization into server environments, it's apparent that this new technology makes backups ever more complicated while at the same time making them more reliable. In this tip, I'll examine how to execute backups with Microsoft Hyper-V by explaining its features and point out a few common problem areas as well.
Server backups with Hyper-V
Think about the two different ways in which virtual machines (VMs) can be backed up. The traditional way for doing this requires installing a backup client into the VM and backing up the VM in much the same way you would with a physical machine. This technique is great when you need to restore individual files, but is of little help if you need to restore an entire machine. Moving to a virtual infrastructure adds the capability to back up an entire virtual machine effectively as a single file. With many of the platforms on the market this means that an entire machine is easily and reliably restored, but getting back individual files is a pain in the neck.
Hyper-V is no different. In fact, Hyper-V comes equipped with integrations such as Windows' Volume Shadow Copies Service (VSS) that makes backing up a machine even more effective than with most other virtualization platforms. This is due to the fact that even with the capability for doing single-file, entire-machine backups using virtualization, the process by which that entire-machine backup works doesn't correctly quiet on-board transactional databases during the period of the backup.
This means that an entire-machine restore of a virtual server which hosts databases like Exchange, SQL or Active Directory is likely to come back with that database in an inconsistent state. The integration of VSS eliminates that problem with Hyper-V by integrating a VSS-aware backup client on the host with VSS writers in
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the virtual machine's operating system. The result is a complete and consistent backup of even the most complex transactional databases.
Implementing VSS for backups in Hyper-V
Hyper-V, being the newest player in virtualization, still has a few idiosyncrasies when it comes to making use of VSS. First and foremost, admins who want to take advantage of this feature must use a VSS-aware backup client. Most enterprise backup clients these days support this capability, but definitely check your support list first.
If your environment doesn't have a VSS-aware backup solution, you can elect to use Microsoft's built-in Windows Server Backup. This Windows Server 2008 "feature" is installed via Server Manager and provides a mechanism for backing up a Hyper-V host server and all of its resident VMs. Note that if you plan to use Windows Server Backup, it is currently limited to backing up entire volumes. In order to make use of its VSS-aware features, you can only back up and restore an entire volume at a time. This can be a major problem if one of your VMs malfunctions and you only need to bring that specific VM back to life.
Regardless of what backup client you choose for your Hyper-V hosts, to turn on VSS-aware backups you'll need to ensure a few things:
Pain points in Hyper-V backups
There are a number of gotchas you should be aware of when it comes to backups. These are not obvious, and can impact where you position your backup clients (On the host versus on the VM versus in both locations). Consider the following:
Hyper-V has some compelling features for virtualization and virtual backups, but it certainly is not without a few caveats. As a version 1.0 release, however, one can argue that Hyper-V's strong VSS support outweighs its limitations.
ABOUT THE AUTHOR:Greg Shields, MVP, is a co-founder and IT guru with Concentrated Technology (www.concentratedtechnology.com) with nearly 15 years of IT architecture and enterprise administration experience. He is an IT trainer and speaker on such IT topics as Microsoft administration, systems management and monitoring, and virtualization. His recent book Windows Server 2008: What's New/What's Changed is available from SAPIEN Press.
