What you will learn in this tip: When it comes to backing up virtual servers within a Hyper-V environment, one of the most frequent questions asked is whether
you should back up the entire host server or back up each individual virtual machine (VM). In this tip, learn about Hyper-V backup best practices, as well as the differences between hypervisor backup vs. VM backup.
Parent partition backups
A parent partition backup is created at the hypervisor level rather than within a VM. One benefit to running parent partition backups is that all of the VMs on the server are simultaneously backed up without the need to back up each VM individually. In the case of a third-party backup application, you might also be able to save money on licensing because you won't need to deploy an agent onto each individual VM.
But using parent-level backups of Hyper-V may have significant limitations depending on which backup application you use. For example, Windows Server Backup can perform parent partition backups once a special registry key has been put into place, but manufacturer Microsoft Corp. places major restrictions on restoring those backups.
In Windows Server 2008, for example, Windows Server Backup only allows you to restore entire volumes and not individual VMs. Although not being able to restore an individual VM is a pretty extreme limitation, some of the third-party backup products have similar limitations when it comes to parent partition backups. For instance, some of the backup products on the market will allow you to back up and restore individual VMs (at the parent partition level), but will not allow the restoration of granular data within a VM. In other words, if you want to get back a file that was accidentally deleted, you would have to restore the entire VM to retrieve it.
That isn’t to say that all of the backup products on the market have such limitations. Over the last year, some backup products have emerged which allow granular restoration of items within VMs backed up at the parent partition level. But such products still place significant restrictions on the VMs involving the VSS writer for Hyper-V, such as lacking the ability to back up a VM that uses dynamic disks (which are different from dynamically expanding virtual hard disks).
Child partition backups
With so many restrictions and limitations on parent partition backups, child partition backups might be a better choice in some cases. Child partition-level backups are backups that are created within an individual VM.
In many ways, child partition backups work just like backups of physical servers. It is worth noting that if you have to restore an entire VM, then you will have to manually create that VM before the restoration can begin. That’s because a child partition-level backup does not back up the VM’s configuration (such as the number of virtual processors and the amount of memory that has been allocated to the VM). So if you plan to use child partition-level backups exclusively, you will have to document the configuration and virtual network settings for each VM.
Other Hyper-V backup best practices
As I stated earlier, there are some third-party backup products that are capable of performing parent partition backups and support granular restorations. Such products offer a combination of the advantages of parent and child partition backups. Even so, there are some Hyper-V backup best practices that you need to know.
First, nearly all Hyper-V backup products are VSS-based. This allows VMs to be backed up while they remain online. However, this only holds true for VMs that are running the Hyper-V Integration Services. Older Windows -- and non-Windows -- operating systems are not capable of running the Integration Services. As such, these types of VMs must be forced into a saved state before they can be backed up.
Another concern is application awareness. If you are running database applications within your VMs, then the backup application must have a VSS writer for those specific applications. Otherwise, the data will be backed up into an inconsistent state (assuming that the VM remains online).
This is especially true for Exchange Server and SQL Server. If the backup application does not have a VSS writer for your database-driven applications, then you may have to back the VMs up at the child partition level or take those particular VMs offline during the backup process.
About the author: Brien M. Posey, MCSE, has previously received Microsoft's MVP award for Exchange Server, Windows Server and Internet Information Server (IIS). Brien has served as CIO for a nationwide chain of hospitals and has been responsible for the Department of Information Management at Fort Knox. You can visit Brien's personal website at www.brienposey.com.
This was first published in October 2011