In my work with Hyper-V beta and with the release candidates, I have needed to recover virtual machines (VMs) that we tested. Most vendor products -- even Microsoft Data Protection Manager -- did not support the Hyper-V Volume Shadow Copy Service (VSS) writer that allows for online, transparent backups at the host level. So I needed an alternative. Even after some vendors began to support VSS, I continued to use alternatives for particular workloads. Why? They work and provide an excellent free- or low-cost way to provide a stable recovery point for all VMs on a host.
This two-part series focuses on two technologies: Windows Server Backup and the Diskshadow utility, both of which come standard in Windows Server 2008. They work with a non-Hyper-V VSS writer application to provide long-term tape backups. Ideally, an application that is aware of Hyper-V VSS could perform backups on VMs that run without interruption. But if your organization has invested in a backup system that is not VSS-aware or has a large environment where the backup application is handling everything from HP-UX to three generations of Windows, then it may not want to add another backup product. The offerings discussed in this series allow you to use your current backup setup and ensure reliable online backups of VMs using the Hyper-V VSS writer on the cheap.
Tip: Make sure your VMs and hosts are up to date with patches, service packs and integration agents. All three of these will affect how successful you will be with the solutions below.
- At the time of this writing, the new integration agents that come with Service Pack 2 for Windows Server 2008 on the host solve almost all the problems I have had with maintaining stable backups on Windows VMs.
- Virtual machines without integration agents or those that do not support online backups -- such as Windows NT, Windows 200 and Windows XP -- will go into a quick-saved state to perform their backups.
- VMs with dynamic disks or with any file system other than NT File System (NTFS) will not be able to perform online backups.
Windows Server Backup
Windows Server Backup is a Windows Server 2008 feature that must be installed. It can incorporate a registry modification to the key below, allowing live backups of running VMs using the Hyper-V VSS writer.
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\WindowsServerBackup\Application Support\{66841CD4-6DED-4F4B-8F17-FD23F8DDC3DE}]
"Application Identifier"="Hyper-V"
This technology provides a good online backup of VMs but poses issues in terms of backing up files to tape with Windows Server Backup. Since Microsoft no longer supports backing up to a tape device with Windows Server Backup, your backed-up VMs must be accessible in the case of a host crash. Since Windows Server Backup does support removable drives and network locations, you could use a large USB hard drive or back up to an alternate server. This solution is not glamorous. But for a test and development environment where you need to retrieve last week's VMs, it is adequate provided you have plenty of disk space.
Plenty of Microsoft articles and blogs explain Windows Server Backup in greater detail. This tool is a low-cost and easy way to back up Hyper-V workloads. In part two of this series, I will discuss two additional low-cost options that provide greater flexibility and recoverability via the Diskshadow utility in Windows Server 2008.
About the expert
Rob McShinsky is a senior systems engineer at Dartmouth Hitchcock Medical Center in Lebanon, N.H., and has more than 12 years of experience in the industry -- including a focus on server virtualization since 2004. He has been closely involved with Microsoft as an early adopter of Hyper-V and System Center Virtual Machine Manager 2008, as well as a customer reference. In addition, he blogs at VirtuallyAware.com, writing tips and documenting experiences with various virtualization products.
