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Hyper-V Export for Backups

Q: I'm thinking of using virtual machine exports for my backups. Is this a good idea?

A: There's a big difference between an export of a running machine and a backup taken via the Volume Shadow Copy Service (VSS) infrastructure. When a backup is performed through VSS, even at the Hyper-V host level, the VSS infrastructure calls all the VSS writers registered inside the virtual machine, which ensures that the applications can flush data out to disk and pause any changes while the snapshot is created. This ensures the integrity of a consistent backup.

An export of a running virtual machines freezes the state of the virtual machine, including its storage, memory, processor, and device state—which is saved to disk. This approach doesn't perform any special application actions to make sure the data on disk is in a consistent state; however, it doesn't need to because the memory and full state of the virtual machine are also saved (which increases the size of the backup). Another option is to delete the memory part of the export—but then you're left with just the virtual hard disk content as it was when the export was taken, which isn't application consistent and if used would be the same as starting the virtual machine as if it had crashed. In addition, this approach might require integrity and repair operations.

I don't recommend that you use exports for backups. Always use VSS for backups instead.

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