Concepts & Mechanics > Full & Incremental Backup

This chapter describes the differences between full and incremental backup jobs.

Hint: All backup jobs which have been created before the incremental feature had been integrated into SmartBackup are Full Backups. So if you want SmartBackup to behave exactly as it did before (without Incremental backups) just leave the option "Incremental Backup" unchecked for your created backup jobs.

Hint: The incremental feature is only available for backup jobs of type Simple Copy and FTP.

Concept of Incremental Backup

Every time you refresh a backup job a new backup revision is created. This revision physically contains only those files which have changed since the last revision (refresh of your backup job).

Let's have a look at a simple example:

You have selected the following source files and folders to be backed up:

•	"C:\test1.txt"

•	"C:\test2.txt"

•	"C:\test3.txt"

•	"C:\Windows"

Let the destination directory of your backup job be "D:\Backups".

First refresh (Revision 1)

Now if you refresh your backup job for the first time (first revision), all files have changed from the last revision since there is none yet.

The first revision is created and all changed files and folders (which means all of them) are backed up to the directory of the first revision:

•	"C:\test1.txt" is backed up to "D:\Backups\rev1\test1.txt"

•	"C:\test2.txt" is backed up to "D:\Backups\rev1\test2.txt"

•	"C:\test3.txt" is backed up to "D:\Backups\rev1\test3.txt"

•	"C:\Windows" is completely backed up to "D:\Backups\rev1\Windows"

If you refresh your backup job for the second time (second revision), all files in source are compared to the files of the last backup (first revision) using the methods seen in chapter Which files and folders may be changed during a backup? depending on the backup type.

Second refresh (Revision 2)

Let's say files "C:\test2.txt" and "C:\test3.txt" have changed since revision 1 and all others remained the same. Then the second revision is created and all changed files and folders (since first revision) are backed up to the directory of the second revision:

•	"C:\test1.txt" is not backed up to "D:\Backups\rev2\test1.txt", but the last backed up version of this file can still be found at "D:\Backups\rev1\test1.txt".

•	"C:\test2.txt" is backed up to "D:\Backups\rev2\test2.txt". The last backed up version of this file can still be found at "D:\Backups\rev1\test2.txt".

•	"C:\test3.txt" is backed up to "D:\Backups\rev2\test3.txt". The last backed up version of this file can still be found at "D:\Backups\rev1\test3.txt".

•	"C:\Windows" is not backed up to "D:\Backups\rev2\Windows", but the last backed up version of this directory can still be found at "D:\Backups\rev1\Windows".

Further revisions

Over time directories "D:\Backups\rev3", "D:\Backups\rev4", "D:\Backups\rev5" and so on are created with only the changed files since the last revision.

Advantages of Incremental Backups

As you can see at the example above changed files are always copied to new revision directories. So you still have the possibility to restore an older revision of a backup job after creating a lot of revisions. If you accidentally backup a changed file you still have the last backed up version in the last revision. In case of a Full Backup the last backed up version is lost.

Disadvantages of Incremental Backups

As a consequence of creating new directories for every revision containing all the changed files (instead of overwriting them like in the case of a Full Backup) more space on the destination is needed. But this is only true, if you change the files, you want to back up, very oft and you set the number of revision to unlimited ( 0 means unlimited ).

IMPORTANT! Specials of Incremental Backup realization in SmartBackup

Generally an Incremental Backup in SmartBackup follows the concepts above, but there is one big difference:

Files that have not changed since the last revision also show up in the directory of the new revision. So if you have a look into one of the revision directories you always see all the files and folders that are contained in your backup job.

Internally the files that have not changed from revision to revision is not physically recreated (copied) but only a link (hardlink) to the file in the directory of the last directory is created which does not consume any more space on your disk. So although the file would show up in many directories it only consumes space once. Incremental Backup is only available on NTFS file systems. In most cases it is recommended to use this type of backup instead of Exact copy type.

So the above example has to be amended to the following:

First refresh (Revision 1)

If you refresh your backup job for the first time (first revision), all files have changed from the last revision since there is none yet.

The first revision is created and all changed files and folders (which means all of them) are backed up to the directory of the first revision (physically copied):

•	"C:\test1.txt" is backed up to "D:\Backups\rev1\test1.txt"

•	"C:\test2.txt" is backed up to "D:\Backups\rev1\test2.txt"

•	"C:\test3.txt" is backed up to "D:\Backups\rev1\test3.txt"

•	"C:\Windows" is completely backed up to "D:\Backups\rev1\Windows"

Second refresh (Revision 2)

Let's say files "C:\test2.txt" and "C:\test3.txt" have changed since revision 1 and all others remained the same. Then the second revision is created and all changed files (since first revision) are backed up to the directory of the second revision (physically copied). The files which have not changed are linked to the directory of the second revision:

•	Hardlink "D:\Backups\rev2\test1.txt" is created which points to "D:\Backups\rev1\test1.txt". Now in you file browser at "D:\Backups\rev1\test1.txt" and "D:\Backups\rev2\test1.txt" the same file shows up (but it is physically the same file which consumes space of one file only).

•	"C:\test2.txt" is backed up to "D:\Backups\rev2\test2.txt". The last backed up version of this file can still be found at "D:\Backups\rev1\test2.txt".

•	"C:\test3.txt" is backed up to "D:\Backups\rev2\test3.txt". The last backed up version of this file can still be found at "D:\Backups\rev1\test3.txt".

•	For every file contained in "D:\Backups\rev1\Windows" a hardlink in "D:\Backups\rev2\Windows" is created which points to the corresponding file in "D:\Backups\rev1\Windows".