365BackUp Keeps Multiple Versions of Each File

Every time your files change, the new versions of each file will be backed up automatically. But that doesn't mean we discard previous versions. In fact, the service will keep three previous versions by default, and can be set to keep up to 28. This is a very effective method of file management in case there is a need to restore a previous version of a document.

Do multiple versions of files = more storage space?

No. These new versions are usually much smaller than the original file - a fraction of the size. Our online backup engine compares each new file against the last version stored. It then extracts the changed data to create a "delta" file. This delta is stored securely on our remote backup servers as a separate version of the file. You can later recover the original file or any of the versions while using only a fraction of the storage space.