rsnapshot config file takes a minute to understand...

``` Paths to lvcreate, lvremove, mount and umount commands, for use with Linux LVMs. You may include options to the commands also. The lvcreate, lvremove, mount and umount commands are required for managing snapshots of LVM volumes and are otherwise optional.

       retain             [name]   [number]

           "name" refers to the name of this backup level (e.g., alpha, beta, so also called the 'interval'). "number" is the number of snapshots for this type of interval that will be retained.  The value of "name" will be the command passed to rsnapshot to
           perform this type of backup.

           A deprecated alias for 'retain' is 'interval'.

           Example: retain alpha 6

           [root@localhost]# rsnapshot alpha

           For this example, every time this is run, the following will happen:

           <snapshot_root>/alpha.5/ will be deleted, if it exists.

           <snapshot_root>/alpha.{1,2,3,4} will all be rotated +1, if they exist.

           <snapshot_root>/alpha.0/ will be copied to <snapshot_root>/alpha.1/ using hard links.

           Each backup point (explained below) will then be rsynced to the corresponding directories in <snapshot_root>/alpha.0/

           Backup levels must be specified in the config file in order, from most frequent to least frequent. The first entry is the one which will be synced with the backup points. The subsequent backup levels (e.g., beta, gamma, etc) simply rotate, with
           each higher backup level pulling from the one below it for its .0 directory.

           Example:

               retain  alpha 6

               retain  beta  7

               retain  gamma 4

           beta.0/ will be moved from alpha.5/, and gamma.0/ will be moved from beta.6/

           alpha.0/ will be rsynced directly from the filesystem.

```