Have you ever bought a server or a network-attached storage device? Do you plan to buy one any time soon and have started researching it? Either way, you would’ve come across the term RAID. At first, it can seem overwhelming to understand what this is and how it can benefit you or business. That’s why the goal of this article is to help you know what RAID is, its different levels, its benefits, and more.
What is RAID?
The term RAID stands for redundant array of independent disks. When you dissect this abbreviation, you can understand what it is:
- Redundant: Can contain the same information for better fault tolerance and data duplication.
- Array: All the storage disks are related to each other in some form.
- Independent: Each of it can work as a standalone storage device.
- Disks: A place to store your content.
When you put it all together, a RAID is a bunch of storage devices that may be interlinked to give you better fault tolerance, improved performance, and increased storage. Typically, two or more physical raids are combined to form a logical unit that operates as a single storage device for your operating system.
In other words, when you combine two or more storage disks in a specific way, you can use it as a single unit to increase storage, improve performance, and duplicate data for better fault tolerance.
This RAID can be achieved through hardware or software. When you add more disks and connect them to a raid controller, it is a hardware implementation. On the other hand, when you partition the same disk into multiple logical disks, it is a software implementation. (For more on hardware RAID vs. software RAID, check out this article here at TechGenix.)
When you have many storage devices that act as a single unit, you have the flexibility to configure them in such a way that it meets your goals.
This specific functionality that you give for each disk through configuration or a combination of different techniques is called RAID levels.
The original paper that put together this term defined six levels, starting from 0 to 5. Over the years, other RAID levels such as RAID 6 and RAID 10 have been added, and some organizations even prefer to combine the role of two or more RAID levels to get the functionality they want.
That said, there are no specific standards that you have to follow, and you can have RAID levels depending on your storage needs, and the goals that led you to set up a RAID system in the first place.
Let’s now look at the different RAID levels.
RAID 0 is used to improve a server’s performance. In this configuration, your data is written across multiple disks through a technique called striping, and each of these disks can read or write data simultaneously, thereby increasing the I/O performance.
The downside is that there is no data redundancy, so if one disk fails, it can impact the entire array. Also, there is a high chance of data corruption or loss.
RAID 1 is used to provide fault tolerance. In this configuration, a technique called data mirroring is used where the data of one disk is mirrored or copied into another. This way, when the primary disk fails, the secondary disk can take over and provide the same data seamlessly. This is the most basic implementation of fault tolerance.
The downside is that performance is slow when you implement RAID 1. Also, there’s an additional cost involved. If you choose to partition a single device into two to implement RAID 1, the amount of available space will also be halved.
RAID 2 is used for error correction. It uses striping where data is spread across different devices, and some disks contain error checking and correcting (ECC) information. It uses something called a Hamming code parity, where a set of error-correction codes or bits are inserted to detect errors that can occur when data is moved to another storage device.
That said, RAID 2 is no longer used as it is similar to RAID 3 and has no significant advantage over the latter.
RAID 3 also works well for error correction and uses the striping method to store data across different devices. The critical difference between RAID levels 2 and 3 is that there’s a dedicated disk for ECC that is used to detect errors in RAID 3. This configuration makes data recovery simple as it calculates the parity information on other disks and compares it with ECC to identify errors and report the same.
The downside is that RAID 3 cannot handle overlapping I/O, and hence it is best for a single-user system.
RAID 4 is similar to RAID 3, except that it supports larger stripes and hence faster overlapping I/O for reading operations. But overlapping I/O for write operations is not possible since all write operations have to update the parity information.
Due to this reason, its use is highly limited and works best in single-user systems where the user wants to read long records from the same drive.
RAID 5 is the most popular configuration used in enterprises and NAS servers as it provides both high performance and fault tolerance.
In this configuration, data and parity information are stored together and are spread across different disks, so even if one fails, the data can be seamlessly re-created from the others. This reconstructed data will be error-free as well due to the parity block present in each disk.
This configuration allows the simultaneous read and write of data, so the performance is better too.
The downside is that performance will be negatively impacted when a server has to perform many write operations as the data has to be duplicated across many servers. Also, it could take some additional time to reconstruct data from backup devices due to the parity check.
RAID 6 is relatively similar to RAID 5, except that it adds another parity that’s distributed across all drives. This configuration helps when two or more disks fail.
Honestly speaking, it is rare for two or more disks to fail at the same time. Another downside is that it is much slower than RAID 5, so it is not used much in the real world.
RAID 10 combines RAID 0 and RAID 1 to offer better performance as it uses both mirroring and striping. In this configuration, the mirror is followed by the stripe, and this provides both redundancy and improved performance. However, a minimum of four arrays is required in this configuration, where the first two mirrors the data while the remaining two stripe them for improved performance.
Due to these advantages, RAID 10 is a popular level in enterprises that handle sensitive information and those that require high transactional databases.
Custom combinations of RAID levels
In the real world, individuals and organizations may need custom RAID levels to meet their specific needs, and they tend to combine different levels to get the benefits that come with each.
Some popular combinations are:
This configuration combines the parity of RAID 5 with the striping of RAID 0 to give improved performance and protection.
In RAID 01 configuration, two disks stripe the data while the remaining two mirror the striped disks with each storing half the data.
This RAID configuration combines RAID 3 and RAID 4 but adds caching. Sometimes, it even comes with a real-time embedded controller and other features that mimic a standalone computer.
This is, in fact, a proprietary configuration that was owned by Storage Computer Corp. (now defunct).
RAID levels: Now you know
As you can see, RAID is an array of disks that enhance performance, improve storage capabilities, and provide fault tolerance. It is used by businesses of all sizes to securely store their data and access it quickly when needed.
These disks can be configured in many ways to meet the goals of an organization, and these configurations are called RAID levels. There are many RAID levels such as RAID 0,1,2,3,4,5,6,7, and these can also be combined to create RAID levels such as RAID 10, RAID 50, and more to meet the specific needs of your organization.
In general, RAID 0, 1, and 5 are suitable for small to medium-sized businesses, and RAID 10 is ideal for large companies that need both fault tolerance and performance. RAID 1 would be ideal for home users as it mirrors data.
It’s important to note that RAID is not a substitute for backup, and that process should happen as usual, though RAID arrays can be a part of the backup strategy.
So, which of these combinations have you used? Do share your thoughts in the comments section.
More RAID levels articles
- RAID 5 vs. RAID 6: When to use each level and why
- RAID 10 vs. RAID 5: When to use each level and why
- RAID 1 vs. RAID 5: When to use each level and why
- RAID 0 vs. RAID 1: When to use each level and why
- Hardware RAID vs. software RAID: Pros and cons for each