There are other options, though. For upgrades, a virtual machine snapshot is a perfect backup, and with really large databases, you would likely have something

There are other options, though. For upgrades, a virtual machine snapshot is a perfect backup, and with really large databases, you would likely have something using WAL archiving, which provides a continuous backup until the point that you shut down the database for upgrade. Finally, if you have a database replica, that can also functionally act as your backup.