@Pagemakers
You are right: incremental backups can and often will need more disk space.
The problem with incremental backups is that you need a "base backup" (i.e. a full backup to start from), with some incremental backups (i.e. backups of "changes") to complete it.
In essence, that method is (normally) not a problem, at least in theory and/or in situations in which the data to be backed up continually grows.
In practice, the following can occur:
a) data present in the "base backup" is changed and, as a result, some incremental backup file is created: the theoretical advantage of having an incremental backup process is reduced, if and only if the static "base backup" cannot be changed. In most incremental backup software, the base backup file is static of nature.
b) data changes are "negative", in the sense that the amount of data to be backup up is reduced to some set of data that is already present in previous backups: even though one should suspect that the incremental backups should not be made, if often is the case that the "negative changes" still lead to a "positive incremental backup" that uses disk space.
The above is a general remark about incremental backups and it depends on the software or code to what degree the above applies.
In general, most incremental backup software is not "smart", in the sense that backups are static and therefore that changes will lead to new disk space usage.
What happens in your case?
Well, your case is one that exhibits the following: a base backup, augmented with some incremental backups, with the sum of those incremental backups being similar to the base.
In every sense, that is
not a waste of disk space in the long run, if
and only if there are only "positive changes", meaning that data to be backed up increases.
For instance, consider the following that applies to an illustrative incremental backup:
Day 0: base backup, 10GB
Day +1: incremental, 2GB
Day +2: incremental, 0GB (note: with most incremental backup software, a 0GB incremental will not occur.)
Day +3: incremental, 7GB
and compare the above to a regular backup, executed every day:
Day 0: backup, 10GB (naturally, this is a backup file, identical to the base backup mentioned above)
Day +1: backup, 12GB (assuming the incremental only contains "positive changes", meaning that data to be backed up increases)
Day +2: backup, 12GB
Day +3: backup, 19GB (assuming the incremental only contains "positive changes", meaning that data to be backed up increases)
and
now compare it to a regular backup with one-day backup retention (for the sake of illustration)
Day 0: backup, 10GB, total disk space used: 10GB (disk space used by the incremental backup process: 10GB)
Day +1: backup, 12GB, removing Day 0 backup, total disk space used: 12GB (disk space used by the incremental backup process: 12GB)
Day +2: backup, 12GB, removing Day +1 backup, total disk space used: 12GB (disk space used by the incremental backup process: 12GB)
Day +3: backup, 19GB, removing Day +3 backup, total disk space used: 19GB (disk space used by the incremental backup process: 19GB)
In short, no harm done when there are only "positive changes": an incremental backup has positive effects (low traffic and faster backup speed) AND negative effects (a lower recovery speed, which is the result of the fact that backup recovery involves multiple backup files).
The above are more general advantages and disadvantages of incremental backups, but note that the
major advantage of incremental backups is that you can allow for a "point-in-time" restore of backups, i.e. you can choose to restore files as they were present on a specific date or time, equal to the backup time (for instance, a backup at Day +1). This major advantage is not applicable to regular backups.
For the sake of illustration, let´s continue and
relax the assumption that only "positive" changes are present.
Consider the incremental backup:
Day 0: base backup, 10GB
Day +1: incremental, 2GB
Day +2: incremental, 0GB
Day +3: incremental, 7GB
and the regular backup (executed every day, with one-day retention):
Day 0: backup, 10GB (naturally, this is a backup file, identical to the base backup mentioned above)
Day +1: backup, 9GB (this often occurs when files, belonging to the base backup are removed)
Day +2: backup, 9GB
Day +3: backup, 13GB (some "positive changes" and some removal of files, belonging to the base backup)
Naturally, you end up with a 13GB disk space usage for the regular backup process and a 19GB disk space usage for the incremental backup process.
It must be clear by now that the above comparison is often applicable, since not all incremental backup processes are "smart", in the sense that "static" backups are used.
The problem is that it is hard to tell whether an incremental backup process is "smart", but if the incremental backups exceed regular backups, then it is not smart at all.
Finally, we
still cannot discard the advantages of the incremental backup process and revert to regular backups.
After all, when increasing the retention rate for the regular backup process, the total disk space used by the regular backup process will also increase, making it less attractive, when compared to the incremental backup process.
In conclusion, one should choose carefully between incremental and regular backup processes, it is not only a matter of disk space.
Try to consider all advantages and disadvantages of both processes
in the context of your own situation, before making a choice or drawing a conclusion.
I hope that all the above helps or explains a little bit.
Regards...
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