Eitex IT Support

Backup Basics

Data Backups - a necessary part of risk management

With the increasing risks of computer viruses, cyber-vandalism and hardware failure, implementing a systemised data backup plan is a necessary part of any business' strategy for risk management.

Data loss can occur because of a multitude of other reasons too, such as accidental file deletion, and may go undetected for days, weeks or longer. A good backup strategy needs to allow you to restore data from a variety of instances back in time.

Tape backups - the ideal medium

Tape is an ideal medium for backing up data because of its high storage capacities, low cost, and the ability to store cartridges off-site.

Organizing a number of tapes into an efficient backup library also allows you to restore data from different points in time, and archive data.

Tape formats

A number of different tape formats exist. Some common formats include:

Tape Formats
Format	Data capacity (uncompressed)	Data transfer rate	Applications
Travan 1	20GB	1Mb/sec	Home use, low range servers
DAT / DDS / 4mm	20GB	2.75Mb/sec	Low range servers, small business
AIT (Advanced Intelligent Tape)	15-50GB	3Mb/sec	Low to mid range servers
LTO (Linear Tape Open)	200-1600GB	40-320Mb/sec	Mid to high range servers and mainframes

The average small business and organization will find that a 4mm DDS tape will provide the solution in terms of data capacity and cost. All data will generally fit onto a single tape, meaning that a single stand-alone tape drive can be purchased (instead of more expensive options such as tape autoloaders, etc)

When should backups take place?

Backups should ideally take place outside of business hours, when network traffic is at its minimum. Scheduling the backup at some time during the night (eg. Midnight) is a suitable tactic for most organizations. Backing up data once a day (after each working day) provides good coverage against data disaster.

Different types of backups

Different types of backups are available in backup software. Each will backup different amounts of data, and different types of files as summaried below:

Different types of backups
Backup Type	Files that are copied over to backup media
Full	All files, system data, etc.
Differential	All files added or changed since the last full backup
Incremental	All files added or changed since the last full, differential or incremental backup
Daily	All files added or changed on the day of the backup

A Full backup will copy all files and system data to the backup media. It allows for the complete restore of all data from one single tape.

Differential, Incremental and Daily are partial backups are designed to reduce amount of data backed-up to the media, resulting in faster backups. To restore data using one of these backups, the last Full backup tape will also be required, along with any other partial backups since the last Full backup.

For example, if Full backups are performed on Mondays, and Incremental backups on the other days, to restore last Thursday's data, 4 tapes would be required (Monday full + Tuesday incremental + Wednesday incremental + Thursday incremental).

The problem with partial backups is the requirement for multiple tapes when restoring data. If any of these tapes is faulty, then the restore cannot be guaranteed to proceed correctly.

Clearly, if all your data can fit onto a single tape, performing full backups all the time is the safest strategy.