Three Important Truths About RAIDs: Redundancy, Failure and Backup

This article was written by Mike Cobb, director of engineering, DriveSavers Data Recovery (DriveSavers, Inc.)

Redundancy, Failure and Backup: Three Important Truths About RAIDs

At DriveSavers, we’ve seen our share of RAIDs. In fact, the company has performed tens of thousands of RAID data recoveries in our history.

We’ve also heard our fair share of stories about RAIDs – some accurate and others, not so much. Although systems typically have redundancy built in, which serves to help lessen the risk of losing data when a drive fails physically, RAIDs aren’t backups. In fact, despite the word ‘redundancy’ being the first letter of RAID (redundant array of independent disks), not all RAIDs even have redundancy incorporated.

More about these common myths about RAIDs.

Myth: All RAIDs have redundancy incorporated
Most RAID setups provide redundancy, in which the same data is located on different drives. This is beneficial because if a drive fails, it can be replaced without loss of data or interruption of work and basic physical maintenance can often be performed (i.e. swapping older drives before they crash, etc.) without interruption to work.

Although redundancy is one of the two biggest reasons users choose to use RAIDs – the other being performance – not all RAIDs actually have redundancy incorporated. For example, a RAID-0 setup – which is used for performance – involves striping data across two or more drives so that different pieces of a single file live on every drive in the system. This RAID setup does not include copies of the data and, therefore, is not redundant. So, regardless of how many drives are incorporated into this setup, if one drive experiences a physical failure, the whole RAID is immediately inaccessible and data is lost. In fact, for this reason, the chances of losing data are actually multiplied when using a RAID-0 as opposed to a single drive.

Myth: RAID failure is always obvious
If a single drive in a RAID with parity or redundancy in place fails, users have access to all of their data. Although the system will continue to run in degraded mode at lower performance speed, the user may not notice that anything has changed. The user would carry on, happily unaware, until the next drive fails.

A dedicated system administrator who regularly and systematically checks a RAID for any problems or concerns may recognize when one of the drives has failed and replace it before any further failures occur. But what if two or more drives fail at once?

Myth: RAIDs are backups
RAID-5, RAID-6 and mirrored systems typically have redundancy built in. This serves to help lessen the risk of losing data when a drive fails physically. However, these devices most certainly are not backups. If too many drives fail, a user accidentally erases files, the RAID gets corrupted or malicious programs take control and encrypt the contents, data can be lost forever.

Unfortunately, many users see RAID and make the terrible assumption that they are protected. When you purchase a complete RAID system, all of the drives that make it up are usually the same make, model and age. Identical drives tend to have very similar, or even identical, life spans. Don’t forget that, while one failed drive may not cause you to lose data, multiple failed drives certainly will.

Most of the RAID systems we’ve seen at DriveSavers over the years have had redundancies built in, but have still had data corruption, multiple failures, or either targeted or accidental deletion of data. The truth is, even RAIDs need to be backed up. If the data loss would be too devastating, then make sure to find a solution to copy data to another media, such as another RAID, the cloud or tape – anything that will ensure that the data is protected when your RAID fails or you experience another data loss situation.