The backups are encrypted, but the there is no way for the backup software to know one client's data from the other. Its block based, so all it sees is a volume.
Post hosting providers, or anybody really don't create new volumes for each customer. They would simply have a directory per client. Onces you start needing to know more about the file system then you sort of waste all the benefits block based backups provide.
By block based I mean volume based, were we simply copy the allocated blocks of the file system that changed between each backup.
