A system and method for performing a point in time backup is presented. A backup application initiates a point in time backup whereupon a backup tracker monitors write requests during the point in time backup. The backup tracker logs data block locations that have already been backed up whose content changes in response to a write request. After a first pass of backing up data blocks, the backup application backs up the changed data blocks. During the changed data block backup procedure, the backup application invokes a copy on write command for particular changed data blocks that receive write requests prior to their content being backed up. The copy on write command stores the particular changed data block's content in a temporary storage area in which the backup application retrieves when the backup application is ready to backup the particular changed data blocks.