However, if the new file is built in stages over a period of time, interim backups should be made at each stage of creation. Additional copies should be created of any modified file after the modification is complete. If the modification occurs over an extended period of time, interim backups should be made at convenient intervals. Due to changing technologies and deterioration of media over time, even if a file has not been used or modified recently, you should make backups of the file on a regular basis. The number of generations to keep depends on your needs.
Some people like to keep, for example, three generations of backups.
Storage Locations Having multiple backup copies at the same location as the original data is a great convenience if you need to restore quickly, but is inadequate as the sole location of your backup copies. An adequate backup requires copies of your data be stored in multiple geographically distinct locations. Multiple locations within the same room or building do not qualify as geographically distinct locations. A more realistic example of three locations would be, for example, your office, your home, and the computer center. The environment of each location is also an important consideration.