ACRONIS Backup & Recovery 10 Server, Windows Guide de l'utilisateur télécharger pdf (Page 22)

It is widely accepted that a full backup is the slowest to do but the fastest to restore. With Acronis

technologies, recovery from an incremental backup may be not slower than recovery from a full one.

A full backup is most useful when:

 you need to roll back the system to its initial state

 this initial state does not change often, so there is no need for regular backup.

Example: An Internet cafe, school or university lab where the administrator often undoes changes

made by the students or guests but rarely updates the reference backup (in fact, after installing

software updates only). The backup time is not crucial in this case and the recovery time will be

minimal when recovering the systems from the full backup. The administrator can have several

copies of the full backup for additional reliability.

Incremental backup

An incremental backup stores changes to the data against the latest backup. You need access to

other backups from the same archive to recover data from an incremental backup.

An incremental backup is most useful when:

 you need the possibility to roll back to any one of multiple saved states

 the data changes tend to be small as compared to the total data size.

It is widely accepted that incremental backups are less reliable than full ones because if one backup

in the "chain" is corrupted, the next ones can no longer be used. However, storing multiple full

backups is not an option when you need multiple prior versions of your data, because reliability of an

oversized archive is even more questionable.

Example: Backing up a database transaction log.

Differential backup

A differential backup stores changes to the data against the latest full backup. You need access to

the corresponding full backup to recover the data from a differential backup. A differential backup is

most useful when:

 you are interested in saving only the most recent data state

 the data changes tend to be small as compared to the total data size.

The typical conclusion is: "differential backups take longer to do and are faster to restore, while

incremental ones are quicker to do and take longer to restore." In fact, there is no physical difference

between an incremental backup appended to a full backup and a differential backup appended to

the same full backup at the same point of time. The above mentioned difference implies creating a

differential backup after (or instead of) creating multiple incremental backups.

An incremental or differential backup created after disk defragmentation might be considerably larger than

usual because defragmentation changes file locations on the disk and the backup reflects these changes. It is

recommended that you re-create a full backup after disk defragmentation.

The following table summarizes the advantages and shortcomings of each backup type as they

appear based on common knowledge. In real life, these parameters depend on numerous factors

such as the amount, speed and pattern of data changes; the nature of the data, the physical

specifications of the devices, the backup/recovery options you set, to name a few. Practice is the

best guide to selecting the optimal backup scheme.

Parameter Full backup Differential backup Incremental backup

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ACRONIS Backup & Recovery 10 Server, Windows Guide de l'utilisateur Page 22