Occasionally you hear the words “I don’t need backup, I have RAID!” or similar phrases. You may have even used them yourself once or twice. They are not the same. Though both are intended to maintain uptime, they perform two different functions which serve two different purposes. Both of them are defense mechanisms against disaster, but to view them as the same is wrong and will inevitably backfire.
RAID – Redundant Array of Inexpensive Disks
RAID is all about defending disaster in the Here and Now. RAID defends against disk failure and allows your system to continue running (albeit at reduced performance) until the disk is replaced and the array is rebuilt.
In the event that you suffer from data corruption, data loss or become the victim or a virus or malware, RAID does absolutely nothing.
Backups exist to provide historical record of what your system looked like at the time the backup was run. There are, at the core of the concept, two backup types: A full backup and an incremental backup. Most organizations will run a full backup regularly during quiet times (e.g. every week over the weekend) as they take a while and can tax resources, and incremental backups which can be less intensive to fill in the gaps (e.g. nightly). There are also other backup systems such as CDP which allow a full backup to be taken and then keeping track of all changes as they happen – they are out of scope for this text.
The purpose of a backup is to grant access to data that has been lost or changed and needs to be retrieved, whether it be a file, a directory, or an entire system. Backup is wonderful for restoring a system that has been compromised or had hardware failure necessitating a reinstall, but it does absolutely nothing to protect a system during the incident, it only helps to recover from disaster.
So you see, RAID and Backup are not the same. Having one is good, but knowing why you have it is better, and having both is better still. And remember, a backup system is only as good as the last backup you tested. If you never test the backup, you’ll never know if it works. And a broken backup system is worse than having no backup at all.