I know that VSS is designed to create a snapshot of the state of the entire system as soon as you call begin backup, and hold on to it until the backup is ended (or the disk runs out of space). Does that mean that as soon as begin backup returns successfully, all of the quiesced or cold shutdown services can be immediately restarted rather than waiting until the backup is completely finished?
Basically, I'm not sure if VSS functions like a filesystem or VM snapshot, or if you have to keep things off for the entire period to ensure correct, always-completing backups. No commercial backup product seems to support this behavior, only having post-backup scripts instead post-backup-start scripts, which is the main reason I'm doubting my understanding, but it's very possible that commercial products are just calcified and risk-averse.