1. A computer-implemented method for performing incremental block based backups for volume and sub-file level backups, comprising: providing a change block tracking driver component that has a write handler component tracking changed blocks and a device control handler switching changed block bitmaps across various points in times defined by incoming writes against a volume device allowing tracking of block level writes for incremental backups without requiring a target system to be rebooted for a filter driver to successfully attach to all volume device stacks built prior to registering the filter to prevent downtime for a production server serving the target system; maintaining a context of the change block tracking driver as a driver context using a single bitmap that represents the volume being tracked; maintaining the bitmap as the only element to track changes across the volume backups and multiple application backups of multiple applications involving different sub-file level backups; and maintaining a persistent store database for file blocks used by each application of the multiple applications and having an extents table and a file system index table to allow each application of the multiple applications to maintain a respective state and rollback respective changes into the driver context.