What is RAID? Everything You Should Know About RAID Array, Levels, Storage and Servers

What Is RAID?

RAID stands for Redundant Array of Independent Disks. Simply put, it’s the process of using multiple hard drives to make a redundant copy of data. Should a drive in a RAID array fail, the data remains secure through a variety of mechanisms. RAID technology spreads your files over several drives in your workstation or servers to protect your valuable data in the event of a drive failure. How the data is protected varies based on the configured RAID level. We’ll cover that later. 

Brief History of RAID

The term “RAID” (redundant array of independent disks) was coined in 1987 by David Patterson, Garth Gibson, and Randy Katz at the University of California, Berkeley. In 1988, they published a paper titled “A Case for Redundant Arrays of Inexpensive Disks (RAID)”, in which they argued that an array of inexpensive drives could outperform the most expensive disk drives of the time.

The authors proposed combining inexpensive PC hard disks into a network and operating them as one large logical drive instead of using expensive SLED hard disks (Single Large Expensive Disks) from mainframe computers. However, this would increase the risk of hardware failure, so the concept focused on redundant data storage. RAID solutions assume that disk failures will occur from time to time and enable recovery without data loss or interruption of user access. 

Today, most motherboards come with built-in RAID functionality, although not all support every RAID configuration. In the past, software-only solutions were used for RAID, but they were considerably slower. In the late 1980s, the “I” in RAID originally stood for “inexpensive,” but it was later changed to “independent.”

RAID has several benefits, including performance, resiliency, and lower cost. However, some say that the technology has become obsolete in recent years and that alternatives like erasure coding offer better data protection. 

Large storage area networks (SANs) often use floor-standing RAID units that offer extensive storage capacity and substantial cache memory. RAID is commonly used in desktop computers by gamers looking to enhance speed and by business users who prioritize reliability.

The RAID Groups?

RAID Groups combine a collection of disks, commonly two or more similar units, into a unified logical unit. When disks of different sizes are connected to a shared RAID Group, the group operates based on the smallest disk’s capacity. Similarly, when a RAID Group contains different types of drives like SSD, HDD, and SAS, the group’s performance becomes limited by the slowest disk. Building RAID Groups based on each group’s capacity and disk type is extremely important for optimizing storage availability and performance. Check out RAM vs SSD.

For effective communication between servers and storage devices, a LUN (Logical Unit Number) is used to identify the storage devices within the RAID Group. LUN can be made up of various configurations, such as a single drive, multiple storage devices, a full RAID array, or a portion of a single disk. Assigning access and control rights through these logical identities can simplify storage resource management.

As a result, the RAID Groups are merged and integrated to form the storage pools, which enhance performance and make administration easier. Enterprises can easily scale their operations by adding disks or RAID Groups to expand their LUN storage space.

Storage pools bring together different types and sizes of hard drives into a single logical unit, resulting in a larger overall storage capacity. Pools are a type of nested RAID level that effectively virtualizes the underlying RAID configuration. Pools evenly distribute data and workload across the entire pool, providing RAID protection for all the data within the pool.

As an IT infrastructural administrator, it is pretty simple to replace or add disks to the right RAID Group in the event of a drive failure or the need for additional drives. After which, data can be dynamically redistributed among the current drives in the pool.

Organizations frequently require customized settings for each RAID Group in their RAID storage architecture for optimal fault tolerance. These combinations of RAID are known as RAID levels or nested RAID levels or categories.

Why do you Need RAID?

If you or your organization value uptime and accessibility, the RAID system can be highly beneficial. Backups are important for safeguarding your data and protecting against potential disasters. On the other hand, retrieving large amounts of data, like in the case of a hard disk failure, could potentially require several hours. These backups are extremely valuable as they can potentially save users hours or even days of work, preventing any loss of data that has been saved or modified since the last backup. RAID allows you to weather the failure of one or more hard disks without losing any data and, in many cases, without experiencing any downtime.

If you’re facing disk IO difficulties, RAID can be a convenient solution. It helps to reduce the time programs spend waiting for the disk to complete tasks. Using RAID technology can significantly enhance performance by allowing users to access and write information from multiple drives instead of relying on a single disk. Furthermore, when choosing hardware RAID, additional RAM is allocated as a cache, reducing strain on the physical machine and improving overall performance.

RAID Levels

RAID arrays use striping, parity, and mirroring to accomplish data redundancy. Understanding what these processes mean is important to knowing which RAID level to select.

Striping For Performance: is the process of segmenting a file into multiple parties and storing each segment on a different physical disk. This process is great for high I/O operations as data can be concurrently accessed across multiple devices, increasing throughput. But if one drive in the striping array fails, the file will become corrupt. That’s why striping is used concurrently with either mirroring or parity.

Mirroring: is simply copying the data on one drive and replicating it onto a second physical disk. This is the simplest form of RAID and achieves basic data redundancy on one drive, but it doesn’t offer the performance and storage enhancements that can be achieved through striping and parity.

Speed and Fault Tolerance (Parity) Data are striped across three or more drives for performance, and parity is computed for safety. Parity is used within RAID to achieve data redundancy during drive failure. If a drive in the array fails, the parity bit is used to rebuild the array on a new hard drive. The Boolean XOR function is used to rebuild the data stored on the surviving drive along with the parity data.

Selecting a RAID Level

As mentioned earlier, disk mirroring refers to duplicating data across multiple disks, striping involves the distribution of data across multiple disks, and error correction involves storing redundant data to detect and potentially fix errors (also known as fault tolerance). Different approaches can be used in different RAID configurations depending on the system’s requirements.

Diverse levels have unique redundancy forms, so discovering a balance between fault tolerance and speed is often required in certain cases. There are several primary RAID levels, including RAID 0, RAID 1, RAID 5, RAID 6, and RAID 10. While there are other levels, like RAID 3, which are not as commonly used. Now, let’s look into these five RAID levels:

1. RAID 0

At least two drives are required for RAID 0, also known as a striped set or striped volume. The disks are merged into a single large volume, and data is evenly spread over the array’s disks.

Disk striping is the process of breaking up data into smaller pieces and writing them either sequentially or simultaneously over many disks. Striped disks operate faster when configured as a single partition, as several drives may read and write identical data all at the same time. As a result, RAID 0 is often used to boost efficiency.

It is the most affordable and simplest redundant disk design on the market. However, it lacks redundancy, parity, and fault tolerance. As such, problems with any disks inside the array might lead to complete data loss. So, it should only be used for non-critical storage, such as temporary data that has been backed up.

You can create a RAID 0 by setting it up with storage disks of different sizes. However, the amount of storage space added to the array by each disk is restricted to the size of the smallest disk. For example, when a 120 GB disk is ‘stripped’ with a 320 GB disk, the resulting array will have a size of 240 GB, calculated by multiplying 120 GB by 2. However, some RAID configurations allow the remaining 300 GB to be used for other purposes

2. RAID 1

RAID 1 is the best choice when redundancy and data protection are the primary goals. With this kind of RAID, your data is stored on one disk and in a separate copy on the other drives that are accessible. This suggests that even in the event of a disk failure, you can still retrieve your data. This technique offers strong data security together with the storage capacity and writing performance of a single disk.

Since the same data is copied between two drives, this is the lowest rate of RAID redundancy and is sometimes referred to as mirroring. It provides almost double the read efficiency of a single drive but does not provide a write throughput boost. As long as at least one drive is functioning, data is always accessible.

3. RAID 5

Popular configuration that strikes a good compromise between performance and security. It offers quicker reading speeds but maintains the same write rates; it requires at least three disks. RAID 5 gives the arrays, which take up the same area as a single drive, more consistency. This level can also withstand one disk failure. Additionally, in the event of a disk drive failure, parity checksums allow the data to be restored.

RAID 5 has the benefit of being able to withstand one failing disk drive. Because RAID 5 is hot-swappable, the array can work correctly even if one disk drive has to be replaced at a time. RAID 5 deployments result in a reduction of one drive in the total array storage capacity since the parity checksums use the space of one disk drive. In terms of fault tolerance, RAID 5 outperforms RAID 0 and 1 and provides more total storage capacity than RAID 1 arrays.

4. RAID 6

With double parity added, RAID 6 and RAID 5 are equivalent. As a result, another name for it is a double-parity RAID. A minimum of four drives are required for this setup. With the exception of two additional parity blocks that are distributed across the drives, the setup is comparable to RAID 5. As a result, block-level striping is used to disperse the data throughout the array, and two parity blocks are kept for every data block.

When striping is done at the block level using two parity blocks, two disk failures are allowed before data is lost. In the event that two drives fail, it is implied that the RAID controller might still reconstruct the necessary data. The implementation of the array and the quantity of disks affect its performance. Writing procedures are slower in double parity configurations than in other configurations.

5. RAID 10

In RAID 10, at least two RAID 1 sets are placed inside a RAID 0 configuration. Performance and enhanced fault tolerance are combined in this way. If your mirrored copy is undamaged, mirroring adds additional redundancy and lets you save the content even if you lose 50% of your disks. Businesses and other pro-units use RAID 10 when stability and dependability are critical for intense procedures.

RAID 10 uses logical mirroring to replicate data across two or more drives in order to provide redundancy. The data is duplicated and stored on multiple disk drives in case one disk fails. The array distributes data blocks across many drives using block-level striping. The ability to access data simultaneously from several drives improves the efficiency as well as reading and writing rates.

RAID Levels: Table

Now that you understand basic RAID terms and their levels. Let’s review RAID levels with a brief description for each:

Basic vs. Premium RAID

At ServerMania, we offer several RAID levels during checkout, depending on how many storage drives you select. Depending on the RAID level you wish to set up and your requirements, you may wish to opt for premium RAID to ensure you receive the maximum performance from your RAID array.

Here is an overview of the options we offer:

Hardware RAID vs. Software RAID

RAID systems may be controlled by a dedicated hardware chip, or the hardware that comes standard with the server may handle the operations involved with RAID controllers.

Only the most basic forms of RAID are available via software control, and most experts agree that there is a performance hit when RAID tasks are handled by software. In nearly every case, hardware RAID is the way to go.

Wrap Up

Each project is unique and requires a different RAID level. It’s important to consider what your goals are in setting up a RAID array. Are you more concerned with data redundancy, performance increases, or both? What is your budget? How much data are you looking to store? These are all important questions to ask, and should help you decide on the appropriate RAID level for your specific use case.

If you’d like to leverage our two decades of experience to choose the perfect RAID setup for your project, book a free consultation. We’ll analyze your needs and budget to set you up with the best RAID solution. Contact us to get started today.