I just gave an example using 10000.
To read/write from disk the offset sould be multiple of sector size

As suggested
After locking the drive you have to dismount it and get rid of the DOS device
I will use FSCTL_DISMOUNT_VOLUME and DDD_RAW_TARGET_PATH | DDD_REMOVE_DEFINITION | DDD_EXACT_MATCH_ON_REMOVE

and update in this thread