A system and method for providing online data backup for a computer system. In which the computer system includes an intermediate block data container. The computer system may utilize the intermediate block data container to manage data block release during the online data backup process. When the data storage driver receives a request to write a block into a data area that has already been copied by the backup procedure, then the required write is performed without limitations. If the incoming write request is directed to an area not yet backed-up, then the write process is suspended and the current state of the given data area is copied to the intermediate data storage container. When the copy procedure is completed, the system will allow the write procedure to be executed. Thus, the content of the data block at the moment the backup procedure commenced is stored in the intermediate block container. The content will be copied from the intermediate block data container by the backup procedure when required. The block will then be flagged and the backup process may continue.