We have a Windows Server '12 R2 box hosting a couple of HyperV virtual machines. The server has an internal RAID1 for local image backups and a RAID1-equipped NAS attached via iSCSI for "offsite" image backups. (I say offsite because the NAS is in another building, albeit one right next door. There is also a files/data/databases-only truly-offsite backup service running on the HyperV children.)
We are using Windows Server Backup on the HyperV parent to make nightly incremental backups of the host and children to the internal RAID1. I've selected "custom" backup, with the following components specified. The internal RAID1 (E: drive) and the iSCSI NAS (F: drive) are specifically excepted from the backup set, obviously.
--bare metal recovery
--child 1 (online)
--child 2 (online)
--EFI system partition
--System C: drive
--HyperV D: drive
On the NAS, we've created fixed-size VHDxes for the children. Using HyperV manager, we've attached a VHDx to each child. Then, in each child, we've configured Windows Server Backup to do nightly incremental backups to its VHDx.
We'd implemented the internal RAID1 backups a month ago when the server was deployed. The child backups were just set up in the last couple of days. This morning, I checked the HyperV parent's backup and it was still running. It was working on Child2, and the status indicated that it was at about 250GB. Child2 only has a 200GB partition, with about 80GB used, not including the VHDx where its backups are stored.
My guess is that the HyperV parent is not only backing up Child2's 200GB OS partition but also its backup VHDx. (I had assumed that it wouldn't do that.) Either that, or the schedules for the HyperV parent and Child2 overlapped, causing some sort of nonesense. I'm running a HyperV parent backup right now to see what happens.
In the meantime, anyone who'd like to critique or comment on our backup scheme, please feel free to share. (There's not really any points for that part, unless we're doing something egregiously wrong and your input saves us from impending disaster.)