Methods and systems for allowing the backing-up of electronic data, its accessibility in times of need, and the ability to restore this data without denying user access to it while the restoration occurs. Also, the data may continue to be backed-up while it is being restored. One method allows for the removal of duplicated data from within the on or off-site copy and subsequent incremental on or off-site-site copies of the data. In this way, the amount of bandwidth and storage required may be reduced. For example, if there are two sets of files required to run two applications and some or all of these files are identical then only one copy need be made and sent and stored. This also applies where the on-site appliance is connected to more than one client server, such that data which is common to the client servers may only be copied once.