Backup of virtual servers
This is an interesting question, for us, a backup should allow fast recovery of active data, so it should be done frequently. Archiving, on the other hand, can be done less frequently; it is about keeping data passive and little consulted. For security reasons, we always suggest having archives in "read-only" mode in order to avoid cryptovirus problems, for example.
In terms of data protection, it is interesting to set up “snapshots”, which work like a snapshot of your data at a given time. Only modified, or differential, data actually uses space, which is also instantaneous and not very resource intensive.
For virtual machines, we mainly work with Veam which is one of the main professional backup software.