The most efficient way to back up a bunch of small files?

Question

Data synchronization

There are directories with files: 910 thousand files, about 30 GB in total, most of the files are small in a couple of KB.
Changes are periodically made to one or another part of it (files change transactionally).
There is a need to store archive versions of files for some time and have access to them as of a particular moment to a set of files or to a slice of the entire file tree at a point in time.
How to solve this problem in the most efficient way?

Answer 1

fold in some file system thread with copy on write (btrfs, zfs, etc.) and make snapshots after "transactional file changes"