Virtual server backup and recovery FAQ

Virtual server backup and recovery FAQ

When disaster strikes, virtual server backup can save the day. There are three major virtual machine (VM) backup methods: agent-based backup, image-based backup and serverless backup. Each VM backup method plays

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a role in virtualization-based disaster recovery, to help quickly recover and restore VM data. You can also use host-level backups, which provide copies of all VMs on a physical host.

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Still, many administrators find backup management problematic. As server virtualization has gained steam, it’s become difficult to fuse physical and virtual backup tools. Many organizations still resist virtual backup best practices, even though using physical tools for virtual server backup creates VM data recovery problems and slow restore times.

The answers to these frequently asked questions can help you better navigate virtual server backup for Hyper-V and VMware, problems you might encounter with VM backup, and the basics of VM data recovery and protection.

What are some basic virtual server backup strategies?

To protect VM data, you can either adapt traditional backup tools or -- even better -- implement virtual machine backup strategies. Tape backups can bog down resources and the network, especially when you need to restore more than one VM at once. It’s better to use virtual server backup methods such as snapshots, data deduplication or continuous data protection. Each VM has a disk file that must be backed up frequently.

How does a VM snapshot work?

Snapshots aid virtual server backup by providing a point-in-time representation of a VM and its configuration. Typically, a VM does not need to be quiesced (or paused), or taken offline for this process. The more often you take a snapshot, the less VM data you stand to lose, but it can take several minutes to write a snapshot.  Another file records any differences between the current VM state and its state at the start of the VM snapshot, which allows users to access the VM during the snapshot backup process. The snapshot is usually stored to the storage area network, facilitating quick VM data recovery in the event of failure.

What are some common virtual server backup problems?

To prevent VM backup problems, be aware of any buffers or cache related to a VM’s applications and check for synchronization issues with proof-of-principle testing. Ensure that a VM is in a stable state before taking a snapshot, or you could end up with a damaged copy. Also be aware that VMs have to be restored as a single entity, so snapshots don't lend themselves to single-file or folder restoration.

What are the most important steps for data protection and recovery?

Start with virtualization-aware virtual server backup tools. Implementing shared storage also helps with virtual data protection and snapshots. But don’t forget the underlying system. Virtual server backup does not replace the need for bare-metal backups of a hypervisor and operating system. Also consider data deduplication to reduce storage requirements, and use backup tools that encrypt VM data for better security. Finally, have a disaster recovery plan to copy VMs off-site regularly, and plan failover workflows in advance.

What are some tips and tools for Microsoft Hyper-V virtual server backup?

The most important tool for virtual machine backup with Hyper-V is the Windows Volume Shadow Copy Service (VSS). To use VSS, you need a VSS-aware backup client. There are also a few conditions that come with Windows VSS. Network-attached storage must be available during the virtual server backup, you can’t back up data stored on pass-through disks, and you can’t back up iSCSI logical unit numbers that are directly connected to a virtual machine’s OS.

When architecting Hyper-V backup, administrators can make some common VM backup mistakes. It seems convenient to install separate backup agents on each VM, but this approach can drain performance, especially if you have multiple VMs running on a single host. You should also avoid backing up Windows XP or Windows Server 2000, VM backups on older OSes can create downtime. Make sure you have support for Cluster Shared Volumes, and note special disk configurations.

How can I ensure consistency between virtual server backups?

Windows VSS ensures that VM data in a virtual server backup is the same as the data in the original. Slight changes can occur during the copying process, but Windows VSS ensures consistency through data quiescence. VSS has numerous components and requires cooperation with other server components, so it’s best to understand this complicated process before installing Windows VSS. With a solid backup method and Windows VSS, your VM recovery will be faster and more complete.

This was first published in March 2011

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