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It means that Hyper-V notifies the guest OS of creating a checkpoint, the app supporting VSS consolidation ends up the current transactions, goes into a consistent state and the VM checkpoint is created. However, the state of the memory is not copied.

(Microsoft recommends using Standard Checkpoints only in test or laboratory environments or to backup stopped VMs.) The production checkpoints are working due to Hyper-V integration tools in the guest OS and are based on Volume Shadow Copy (Windows) or file system freezing daemon on Linux ( fsfreeze). To solve this problem, a new checkpoint type - Production Checkpoints appeared in Hyper-V 2016. In some cases, it may result in some issues in the OS itself and losing data in the running apps (especially in transaction ones, like Exchange, SQL, ADDS, etc.). So when trying to restore a VM from that backup, the OS tries to continue its operation since the moment the checkpoint has been created. Originally, the guest OS does not know that it is backed up.Based on the points described above, when using external data storage to store VM files, you can use the features of data storage integration with the backup product (such a hardware snapshots).So it is better to use a separate server network or HBA interface for the backup traffic or copy the data over SAN. When copying the VM checkpoint data over LAN from the Hyper-V host to the backup storage, the network may be highly loaded.Thus, you do not need to copy the VM as a whole. In Hyper-V Server 2016, the Resilient Changed Tracking (RCT) technology is used to make backup faster due to copying only the blocks of data changed since the last backup. It means that it is better to copy the checkpoint as quickly as possible. If there are many changes in the VM while the checkpoint is being copied, merging files after deleting the checkpoint may high load the storage subsystem, the Hyper-V host, and the VM itself. The longer the backup tool is copying the checkpoint (backup), the more changes are logged in the delta files.

I will try to list the most common problems: This is general information about the Hyper-V backup, but actually, there are a ton of nuances and issues. Hyper-V VM Backup Best Practices and Requirements If you lose the productive VM, you will be able to recover its state at the point of time when the backup was created. When deleting the checkpoint, Hyper-V consolidates (merges) the original and delta files, in the meantime the VM goes on working. Now the backup tool must copy the original VM files (no changes are written to them) to the backup media and then delete the checkpoint. After receiving the command, the hypervisor creates some new files (delta files) and the VM goes on working and starts saving changes in the files. The backup tool instructs the Hyper-V host to create a checkpoint. Currently, agent backup scenarios are rare, and are mostly used for the specific apps that do not support VSS. In the virtualization era the backup creation point has moved from the guest OS to the Hyper-V host, on which VMs are running. Previously, server backup was performed by a backup agent installed on each host.