Today’s post is from Kathy Davies one of the excellent Hyper-V technical writers. Enjoy!
Here is some preliminary documentation on planning for backing up Hyper-V VMs. It will eventually be made part of our Planning and Deployment guide on TechNet.
Planning for Backup
When you plan a backup and recovery strategy for a virtualized server environment, there are several factors to consider. You must consider the different types of backups you can make, the state of the virtual machine, and the type of storage being used by the virtual machines. This topic discusses the advantages, disadvantages, and considerations for these factors.
Understanding the backup options and considerations
The backup integration service and the Hyper-V Volume Shadow Copy Service (VSS) Writer provide the mechanism for backing virtual machines as well as system-wide settings that apply to Hyper-V. There are two basic methods you can use to perform a backup. You can:
· Perform a backup from the server running Hyper-V. Using this method to perform a full server backup is the recommended method because it captures more data than the other method. If the storage is compatible with Hyper-V and the Hyper-V VSS Writer, you can perform a full server backup that helps protect all of the data required to fully restore the server. The data included in such a backup includes the configuration of virtual machines and virtual networks, snapshots associated with the virtual machines, and virtual hard disks used by the virtual machines. As a result, using this method can make it easier to recover the server if the need arises, because you will not have to recreate virtual machines or system-wide settings such as virtual networks.
· Perform a backup from within the guest operating system of a virtual machine. This method is useful when you need to back up data from storage that is not supported by the Hyper-V VSS writer.
As you plan your backup strategy, consider the compatibility between the storage and backup solutions:
· Virtual hard disks offer the best compatibility and can be stored on many types of physical media. For more information about the types of storage you can use with Hyper-V, see “Hardware Considerations” in the Hyper-V Planning and Deployment Guide on TechNet (http://technet.microsoft.com/en-us/library/cc816844.aspx).
· Network-based storage such as shared folders should be used with caution. If the network-based storage is unavailable when a backup is attempted, the backup will fail.
· Physical disks that are directly attached to a virtual machine (sometimes referred to as ‘pass-through disks’) cannot be backed up by the Hyper-V VSS writer. As a result, this type of disk will not be included in any backup performed by a backup program that uses the Hyper-V VSS writer. In this situation, you would need to use some other process to back up the physical disk. For example, you could run a backup of the data on the iSCSI storage from a backup application running in the guest operating system.
· Storage accessed from a virtual machine by using an Internet SCSI (iSCSI) initiator within the guest operating system will not be included in a backup of the physical computer. In this scenario, you must use another process to back up the data from the iSCSI-based storage before you perform a full server backup. For example, you could run a backup of the data on the iSCSI storage from a backup application running in the guest operating system.
· iSCSI-based storage is supported for backup by the Hyper-V VSS writer when the storage is connected through the parent partition and the storage is used for virtual hard disks.
Understanding online and offline backups
Whether a backup is performed online or offline depends on whether the backup can be performed without downtime.
An online backup can be performed with no downtime on a running virtual machine when all of the following conditions are met:
· Integration services are installed and the backup integration service has not been disabled.
· All disks being used by the virtual machine are configured within the guest operating system as NTFS-formatted basic disks. Virtual machines that use dynamic disks or the FAT32 file system prevent an online backup from being performed.
· Volume Shadow Copy Service must be enabled on all volumes used by the virtual machine with a specific configuration. Each volume must itself as the storage location for its shadow copies and that mapping must be available to the Hyper-V VSS writer. In other words, the shadow copy storage of C: should be on C:, the shadow copy storage of D: should be on D:, so on an so forth.
If an online backup cannot be performed, then an offline backup is taken. This type of backup results in some degree of downtime. A variety of factors can affect the time required to take an offline backup. If the virtual machine is running or paused, it is put into a saved state as part of the offline backup process. After the backup is completed, the virtual machine is returned to its existing state.