The network backup service is an extremely reliable and consistent service, and its multi versioning allows for the best recovery options available. However, when there are network issues during file synchronisation/backup, orphaned files will be created and these fragments are never removed. This fragmentation, over a year can lead to as much as a 10% increase in online storage for backup over less reliable media such as ADSL. 

Annually, on renewal of your services, we perform a refresh. This requires all data to be purged and a fresh initial sync to be performed. As in most cases the majority of online storage never changes, this initial refresh will require a complete copy of the backup medium, after which change synchronisation will continue as usual.