Backups Part 2: basic concepts
Backup blog series table of contents:
We discussed the many reasons for making backups in the previous part of this blog series. It’s obvious that, when going in depth with backups, there’s a lot more to tell. First, we define what a backup is. Next, we list up a few things that are part of the backup terminology.
What is a backup?
A backup is a copy of computer data. These computer data are taken manually or automatically and they are stored elsewhere, preferably not in the proximity of the system itself. Backups can be used in each situation where the loss of data occurs. By restoring the backup, the original data are restored, or the system is reverted to a system state before the malicious event happened. Backups usually are part of a disaster recovery plan, something we will discuss later in this series.
In this shortlist, we go through various definitions that are related to backups. The first part are terms that appear a lot when backups are discussed. The second part discusses other definitions that might appear here and there, but aren’t necessarily part of the “default definition set” of backups. Let’s start with the basics:
Unstructured backup: this is a synonym for a manual backup. It basically means that one takes a copy of necessary files and stores them on a location that is different from the original location. It’s time consuming and you can do it whenever you feel like it, hence the name “unstructured”. Because this happens manually, people could forget about this, which makes this method of making backups unreliable.
Full backup: the system is set up in a way that a complete copy of the target (the data that needs to be backed up) will be made, either at certain points in time, or whenever the user tells the system to do it.
Differential backup: before a differential backup is made, a full backup is made. After that, all changes to files since the last full backup are recorded. This would result into 2 backups at most, which are the full backup and the backup that contains the changes. Restoring this backup also means that only 2 backups need to be restored.
Incremental backup: this is very similar to differential backups, because a full backup is made, and then all changes will be backed up as well. The difference is that changes will be recorded since the last backup. In this case last backup could mean the last full backup or the last incremental backup. Restoring this sort of backup means at least 2 backups need to be restored.
Snapshot: this is a term that applies to virtual machines. Whenever a snapshot is made, a copy of the virtual machine in its current state is made. Saving a virtual machine is the same as saving the files in which the virtual machine is kept.
Next are the other definitions, that could still be important.
Image based backup: instead of backing up raw data, the backup happens on block level and with frequent intervals. A full backup is made, and the full backup is made according to the user defined frequency.
Reverse incremental: a mirror of the source data will be stored, together with the differences between the mirror and its previous states. With this method, the full backup will be synchronized with the live copy, while storing the data necessary to reconstruct older versions.
Backup repository: the storage location where backup files are kept
Near-CDP: CDP means Continuous Data Protection. This type of backup saves a copy of every change made to the data. Restoration of data to any point is time is possible with this method and it’s one of the most comprehensive and advanced methods of data protection. CDP will do the data replication every time the change is made. Near-CDP will do it at set intervals.
System image: a copy of the entire state of a computer system at that moment, that is kept in a non-volatile form, mostly a file. With this backup, a system can be restored or reverted to said state.
Disaster recovery: when something malicious happens, it’s time to recover from that. Companies often create and maintain a plan for disaster recovery. Backup strategies are always involved in such a plan.
By reading this article, you will have the important fundamentals to comprehend backups. But we aren’t there yet, there’s still a lot to come. In the next part, we will discuss the many ways to store backups.