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Backup Types

After you choose your backup medium and backup utility, you must decide what type of backup to run. The types vary by how much data they back up each time and by how many tapes it takes to restore data after a complete system crash. The three backup types are:


■    Differential

■    Incremental

Full Backup

In a full backup, all network data is backed up (without skipping any files). This type of backup is straightforward because you simply tell the software which servers (and, if applicable, workstations) to back up and where to back up the data, and then you start the backup. If you have to do a restore after a crash, you have only one set of tapes to restore from (as many tapes

as it took to back up everything). Simply insert the most recent full backup into the drive and start the restore.

If you have a tape system with a maximum capacity of half the size of all the data on your server, the backup utility will stop the backup halfway through and ask you to insert the next tape. Normally, full backups take several hours, and most companies can’t afford to have a user sit in front of the tape drive and change tapes. So you need a backup drive and medium with enough capacity or a backup system that can automatically change its own tapes (such as a DAT autoloader).

Figure 9.4 shows the amount of data backed up each day in a full backup scheme. Note that if you are working with 20GB of data, approximately 20GB is stored on a new tape each night, along with any additional data from that day. However, you are basically backing up the same data each day.

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