Networking

Incremental Backup

Some companies have a very finite amount of time they can allocate to backup procedures. Such organizations are likely to use incremental backups in their backup strategy. Incremental backups save only the files that have changed since the last full or incremental backup. Like differential backups, incremental backups use the archive bit to determine the files that have changed since the last full or incremental backup. Unlike differentials, however, incremental backups clear the archive bit, so files that have not changed are not backed up.

The faster backup times of incremental backups comes at a pricethe amount of time required to restore. Recovering from a failure with incremental backups requires numerous tapesall the incremental tapes and the most recent full backup. For example, if you had a full backup from Sunday and an incremental for Monday, Tuesday, and Wednesday, you would need four tapes to restore the data. Keep in mind: Each tape in the rotation is an additional step in the restore process and an additional failure point. One damaged incremental tape and you will be unable to restore the data. Table 4 summarizes the various backup strategies.

Table 4 Backup Strategies

Backup Type

Advantages

Disadvantages

Data Backed Up

Archive Bit

Full

Backs up all data on a single tape or tape set Restoring data. requires the least amount of tapes.

Depending on the amount of data, full backups can take a long time.

All files and directories are backed up.

Does not use the archive bit, but resets it after data has been backed up.

Differential

Faster backups than a full.

Uses more tapes than a full backup. Restore process takes longer than a full backup.

All files and directories that have changed since the last full or differential backup.

Uses the archive bit to determine the files that have changed, but does not reset the archive bit.

Incremental

Faster backup times.

Requires multiple disks; restoring data takes more time than the other backup methods.

The files and directories that have changed since the last full or incremental backup.

Uses the archive bit to determine the files that have changed, and resets the archive bit.



by BrainBellupdated
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