The main reason to use online backup is to get data off-site for integrity and protection. Once off-site, it should be stored in perfect condition for Continuous Secure Backup Systems Data Protection.
CRC (Cyclic Redundancy Check) is constantly error checking so files containing errors do not get sent from server to server and replace data in each station.
Online backup companies who do not offer CRC are as good as a faulty RAID system where data is simply mirrored with errors which transfer from disk to disk without being 'screened' first from Raid Disk to Disk.