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What is a RAID?

June 12, 2013 4 min read

What is a RAID? Why do I need a RAID? What do all those mode numbers mean? You may be asking these questions and more. Generally, the answer to the second is the easiest one. For most users who utilize RAIDs, they are in need of a) additional storage and b) redundant data storage. After coming to that conclusion, it is then important to understand what a RAID is and how it differs from an additional standard external/internal drive. RAID stands for "Redundant Array of Independent Disks." This naming is an artifact from a time when high capacity hard disks were still fairly expensive. This was a means by which you could combine multiple small (less expensive) drives in order to make larger, redundant, faster drives at a lower cost. RAIDs have varying levels, but all work by the same basic principle: data is distributed across the hard drives in one of several ways, depending on the level of redundancy and performance one desires.

Fault Tolerance

When talking about RAIDs it is important to remember that they were initially developed to facilitate redundancy (this is also referred to as fault tolerance or failover protection.) This was an important development because it helped decrease the loss of data due to drive failure. If multiple drives are involved and one (or more) fail, the array and the data it contains would remain useable despite the failure. It is not uncommon to hear of RAID setups described by the number of drives that can fail and still maintain data integrity; 1-disk or 2-disk redundancy, as an example.

Hardware Failure

Redundancy and redundant systems have wide applications from small businesses to academic research, because unfortunately drive failures do occur. That being said, while RAIDs do offer some peace of mind, RAIDs offer no protection of data loss against malware, theft, or natural disasters. It is important to note that RAIDs are no substitute for a proper backup routine. RAIDs are, however, excellent for providing a fail-safe against hardware failure.

As mentioned above, RAIDs have varying levels, or modes, by which the drives are conglomerated. They are most commonly referred to by their level number. The four most common arrays the average user will encounter are JBOD, RAID 0, RAID 1 and RAID 5. If you move into larger operations, you will see levels 6, 10 and 5+1 (or more depending on your exact needs.) For this discussion, we will stick with the most common RAID setups.

Common RAID Levels

RAID drives

RAID 0 – The primary function of this setup is speed. This level distributes data across multiple hard drives that permit increased read/write speeds. This approach is often referred to as striping. RAID 0 sadly offers no protection versus drive failure, since this method does not write any duplicate or redundant information. If even a single drive fails, you end up with missing data.

RAID 1 - The primary function of this setup is data integrity or redundancy. This level reads and writes data to pairs of drives. This method is often referred to as a mirrored setup. These drives work in unison with each other. If one fails, you can continue working with the other until you replace the failed drive. RAID 1 is the simplest configuration method for fault tolerance protection for disk storage. However, it does consume 50% of your total disk space. For example, in a RAID 1 setup with 2 x 1 TB hard disks, you do not get a usable space of 2 TB; rather, you end up with 1TB usable storage space.

RAID 5 – This RAID level offers both speed and data redundancy. RAID 5 reads from and writes data to multiple disks, as well as distributes parity data across all the disks in the array. Parity data is a smaller amount of data derived mathematically from a larger set of data. Consequently, it can accurately describe that larger amount of data, and therefore is used to restore it. Because parity data is distributed across all the drives, any drive can fail without causing the entire array to fail. RAID 5 uses approximately one third of the available disk capacity for parity information, and requires at least three disk drives to implement.

JBOD – This is shorthand for "just a bunch of disks." This is not a RAID method, but it is often available as an option on multidisk storage boxes that offer RAID. JBOD offers no speed increase or redundancy. It simply concentrates a group of disks into a single volume. Data is written to the first drive until full, then on to the second, so on and so forth, until the last drive has been filled. This is not a recommended configuration.

RAID in Review

In review, those are the basics for understanding the most common forms of RAIDs. For understanding which RAID is best of you:

  • Assess whether you require more then a simple external or internal hard disk. If possible, use hardware RAID (physical expansion card installed in the machine which has various connector ports) over software RAID. Software RAIDs are fast. However, many implementations rebuild randomly and that can affect performance while in progress.
  • Select RAID 0 if all you are interested in is faster performance and you do not need failover protection.
  • Select RAID 1 when you have two drives and want to protect against drive failure.
  • Select RAID 5 when you have more then two drives and you want to protect against drive failure as well as increase performance.

Ramjet offers a wide selection of RAID products that you can find here. You can always call us at 1-800-831-4569 and we would happy to provide you a technical consultation.