JetBackup can perform several types of backups. We will explain briefly about each one of them.
The "Directories incremental" job will back up the files keeping a "snapshots" based files structure, so you can have several backup retentions of this backup, on supported destinations (SSH / Local / Amazon).
The "Replicate" job, will take the folder "as is", and cannot save backup retentions. Since we are using rsync, the backup process is optimized and only changes from the last full backup will be copied, but you will not be able to have backup retention and to create a "backup history" of your files/folders.
"Point-In-Time" Space Consuming incremental backups - If you choose more then one backup retention - JetBackup will create a "point-in-time incremental backups", in which will use as little space as possible (using hardlinks). So a 30 days backup retention for a 2GB file/directory will consume 2GB + 30 Days of new/changed files (** At the moment, mysql is fully dumped, as it doesn't support incremental backups).
Backup structure: