Most of you have heard sooner or later about RAID. The acronym means “redundant array of inexpensive disks”, or “redundant array of independent disks”. Wikipedia has a rather good quality article on RAID.
The idea behind it is that physical hard drives fail, and when a single drive fails, RAID typically provides a solution to avoid any data loss. A drive is changed but redundancy makes it simple. This is the case for most RAID levels except some like RAID 0 which just makes a single larger drive.
If RAID provides a way to manage the failure of a drive, why is this article named “RAID is not a substitute for backup”? Well there are multiple reasons for that.
Multiple drives can fail at the same time
Yes, multiple drives can fail at the same time. Believe it or not, this has nothing to do with “bad luck”.
Probability that another drive fails before the first failing drive is replaced is low, but not zero. This is a first problem. It can be increased if disks get old and disk health is not monitored. Reconstructing the redundancy after a drive change can also temporarily increase the level of stress to remaining drives. They are used for current operations, and they are read entirely in parallel to reconstruct the redundancy. However, this is not the highest risk.
Drives can fail because they are naturally unreliable, they have limited MTBF, they get old… But they can fail because of an external cause.
Fire, physical shocks, voltage surge… Multiple risks can affect all the drives at the same time.
RAID is not a backup at all
RAID is rather a technology to have multiple drives operating as a larger, more reliable drive.
If you delete a file by mistake, RAID will not change anything. Maybe you can use a recover tool, or maybe it’s too late or too complicated, but RAID doesn’t change anything on that.
If a cyber-attack deletes or corrupts your files, you have the same problem with RAID or without RAID.
A backup needs to be a copy of your data, a backup needs to allow you to go back in time with your data in some way (if you cannot “restore”, it’s not a backup).
So what, should I throw RAID away?
Absolutely not. RAID is a very interesting technology that you can use in conjunction with a backup strategy. Do you have a backup on a NAS? Better if the NAS (network attached storage) uses RAID.
Do you have a server? RAID can reduce the consequences of drive failures.
RAID is very useful, you just need to understand what it is, what it is not, and how to have a solution that works for you. Stay tuned for other articles about RAID! Most importantly I intend to cover basic principles of backups.