Running a bunch of hyper-v virtual machines that matter? You'll want a high availability cluster. Of course you'll also want to take backups of those VMs as well. Prior to moving your VMs into the HA cluster, you were able to take backups of both the host server and its VMs using the included Windows Server Backup program that comes with both Windows Server and Hyper-V Server Core. It works well, although a little light on features, and it's free. Once you move to a HA Cluster, Windows Server Backup will no longer be available to help you.
High Availability is nice for improving up time by providing host server failover, but it doesn't do anything to protect your data. The data storage for an HA Cluster will be a shared storage solution - either SMB 3.0 or a clustered shared volume (CSV). Depending on that storage solution, you may have some data backup in place at that level and I'd assume some level of disk redundancy via RAID 5,6,10 etc. But what about a backup solution that is aware of your virtual machines?
Microsoft System Center
One of the most obvious choices to fulfill this need is Microsoft System Center, specifically the Data Protection Manager component. If you're a bigger company and a Microsoft shop doing virtualization, you likely have this software already. Microsoft basically assumes as much, which is probably why they don't care about Windows Server Backup not working for HA Clusters. Using Data Protection Manager, through its fairly clunky interface, you can backup hyper-v VMs in an HA Cluster without much trouble. You also get the benefit of the extensive virtual machine management and deployment features that come along with System Center. With a price tag of about $3,600 for the Datacenter license (the only one that makes sense to buy), it's not cheap but it's definitely within reach of most companies managing more than just a few servers.
Altaro Hyper-V Backup
If you don't need the enterprise level virtual machine management tools that come with System Center and just want backup, Altaro has a nice solution that you might consider. Depending on how many hyper-v hosts are in your cluster you can save a lot of money over System Center at $395/host for the standard edition and $595 for the unlimited edition. In my case we have 3 hosts in our cluster and we use a CSV for storage which requires the unlimited edition. That brought us to $1,785 for the licence, less than half the price of System Center. It's a full featured backup solution with a central management console, a backup agent for each host, and a modern user experience. It has backup verification and off-site secondary backup capabilities along with granular file restore, custom retention policies, and flexible backup scheduling options. We've been using it for several months without any problems and it's pretty much self sustaining at this point.
An Environment Decision
For us the decision to choose Altaro Hyper-V Backup over Microsoft System Center had to do with the fact that we have a fairly small number of virtual machines to manage, 15 or so. We don't add VMs often so that number is unlikely to grow in any meaningful way over time. If we were running a Virtual Desktop Infrastructure or had pile of VMs to care for, we'd have gone for System Center for sure since it's much more than a backup tool.
There are other options out there as well, if you've got experience (good or bad) with a Hyper-V backup solution, let's hear about it.