Backup and restore systems information

General needs Media Type of backup
Types of events Archive bit Type of strategies

General needs

The two most critical process for survival in today's fast paced computing environment is backing up data files on a regular schedule and maintaining a disaster recovery plan (DRP). A business can not afford to have critical information systems unavailable. Scheduling services, client/customer data, accounting systems, and electronic communication are vital to today's business. Several needs must be accommodated in a backup plan.

Speaking only in computer terms there are several types of catastrophic event.

Other catastrophic events include


Media used for backup.

There are many types of backup media. Tape of all forms have been used since the early days of computing. Tape was the primary form of mass storage before disk based systems. For the most part all medias offer good reliability. The major concern today is capacity. A media that must be changed during backup hinders the progress / execution of the backup. A person must change the media when it is full. Autoloaders are available for any storage needs that are greater than common single tape drives. The falling cost of hard drives has allowed for backing up to an alternate hard drive. Adding a removable drive kit allows for rotation of hard drives. This is a very fast option, so it is suited for rapid backup where recurring down time for backup can be costly, and the backup window is very small.



Archive bit - stored in actual file.

The archive bit is one bit of information that signals whether a file has been backed up. It can be set or reset. Example, - A file is backed up on Monday and the archive bit is reset. The next day the file is modified and the archive bit is set. The next backup will read the archive bit and know to backup the file. If the file has not changed the archive bit is not changed and the file is not backed up. Many flexible backup routines can be developed using just one bit of information. The archive bit is stored at the file level, therefore the changing of the archive bit does change the modified date of the file.


Types of backup - Copy, Full, Incremental, and Differential

Copy - Some backup applications allow for an exact copy of the drive or volume. Generally speaking the archive bit is not changed.

Full - The backup application backs up the target files and the archive bit is reset. If a file is modified the archive bit is set.

Incremental - The application backs up only the files that have the archive bit set, and resets the archive bit when finished.

Differential - The application backs up only the files that have the archive bit set, and does not change the archive bit.


Types of strategies

Having a backup routine and policies that several persons are familiar with is most reliable. Backup routines and policy decisions center around three factors.

1. Reliability - This is the most important decision. An unreliable backup is worse than no backup at all. It is more disappointing and frustrating to realize that the backup is not valid after a restore is performed than to have a failure and no backup. If you have not taken the time to back up, you have no one else to blame. If you have taken the time to backed up and the backup is not valid or non existent, you are disappointed in the system

2. Ease of use - Any backup strategy should be easy to use. If backing up is simple and easy to maintain, it will be done on a regular basis.

3. Speed - Most automated backup systems are configured to run at night or off hours. Can the system finish the backup in the allocated time, is the primary consideration in this type of backup. A backup that is still in process when the data is to be used or needed will not be reliable.