| General needs | Media | Type of backup |
| Types of events | Archive bit | Type of strategies |
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.
Being prepared for limited loss of data (generally user error) is the first need to be met. An on staff person should be familiar with the backup technology, the daily backup rotation and how to restore from the appropriate backup. The on staff person should be able to detect and respond to common error messages from software/hardware, or other backup device failure. This would be included in the DRP.
Every business should have a plan for catastrophic events. This is known as a Disaster Recovery Plan (DRP) and is the second need to be met.
Speaking only in computer terms there are several types of catastrophic event.
Total or intermittent failure of a drive or other component failure preventing the server/workstation from functioning properly and resulting in no data access. Examples include Bering, head, arm and coil failure in the hard drive. Controller card, power supply and motherboard failure can fall into this category.
Failure or intermittent failure of any component that prevents the system/network from operating properly. This includes switches, routers and any component that processes/filters data.
Other catastrophic events include
Denial of entry / access. For some reason you do not have access to your information system. Off site backups will be required. Restoration from offsite backups at an alternate location is required. Common examples of denial of entry / access include fire, flooding, hurricane, tornado's and their associated damage. Unfortunately, after 9/11/01, acts of terror need be considered.
Theft or hostage taking of critical data. Yes, this does happen.
User error. This is the most common source of data loss.
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.
Multiple medias should be implemented.
Tape is the most common and media is widely available.
Hard drive to hard drive backup ( not mirroring ) is fast and reliable, however media cost is high, but dropping.
Hard drive to removable hard drive is fast and reliable, however media cost is still high compared to tape and media durability is questionable if mishandled.
CD-R/CD-RW is slower and must be changed during the backup process if capacity is exceeded. Each disk holds 650-700 MB each. CD-R/CD-RW is very reliable. Media cost is very low.
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.
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.