What is RAID 5? How does it work (2023)

Although it has been around for over 50 years, RAID is still very popular, especially in corporate settings. In general, it is a great achievement that any technology has been relevant for so long.

If we focus on the state of RAID these days, some RAID levels are arguably more relevant than others. RAID 5 specifically has been one of the most popular versions of RAID for the past two decades.

As disk sizes have increased exponentially, this begs the question; Is RAID 5 still reliable? To answer this question, we will first have to talk about what exactly RAID 5 is, its working mechanisms, applications and failures.


RAID terminology

RAID 5 uses block-interleaved distributed parity. To understand this, we'll have to start with the basics of RAID.

(Video) RAID 5 vs RAID 6

Redundant Array of Independent Disks (RAID)It is basically a data storage technology used to provide protection against disk failure through data redundancy or fault tolerance, as well as to improve overall disk performance.

RAID systems implement techniques such as striping, mirroring, and parity.linedDistributes logically sequential blocks of data across all disks in an array, resulting in better read and write performance.

Parity, in the context of RAID, is recovery data written to a dedicated parity disk or spread across all disks in the array. If a disk in the array fails, this parity data, along with the data on the remaining working drives, can be used to rebuild the lost data.

How does RAID 5 work?

Using RAID 5 Arraysblock level hatchingcomdistributed parity. Since at least two disks are required for striping and additional disk space for parity, RAID 5 arrays need at least3disks Let's take a 4-disk RAID 5 array as an example to better understand how it works.

When writing to the array, ablock-sized chunkdata (A1) is written to the first disk. This data block is also calledreach. The block size is calledpart size, and its value varies according to the user definition.

What is RAID 5? How does it work (1)

Continuing with the write operation, the next logically consecutive data block (A2) is written to the second disk and the same for the third (A3). Since the data blocks are distributed over these three lanes, they are collectively referred to as araya.

stripe size, as the name implies, refers to the sum of the size of all the strips or pieces of the strip. Hardware RAID controllers typically use stripe size, but some RAID implementations also use block size.

What is RAID 5? How does it work (2)

Continuing again, after the data is spread across the disks (A1, A2, A3), the parity data is computed and stored as a block-sized block on the remaining disk (Ap). With that, a full track of data was recorded.

(Video) RAID 5, explained

In our example, the same process is repeated again as the data is striped across three disks, while the fourth disk stores the parity data. Simply put, this continues until the write operation is complete.

But there are a few more things to cover here, such as how the parity data is actually computed and the layout of the data and parity blocks in the array. So let's shift the focus to those in the next section.

Parity in RAID 5

Different RAID levels use different algorithms to calculate parity data. RAID 5 specifically uses theExclusive OR (XOR)operator on each byte of data.

XOR returns a true output when only one of the inputs is true. If both inputs are true (1,1) or false (0,0), the output is false. The table below and the example below should better illustrate this.

First entrysecond entrySalida

Let's go back to our previous example and look at the first clue. Let's say the first byte of data in the strips is as follows:


When we carry out an operation A1 XOR A2, we obtain the output 01110011. When we carry out another operation XOR with this output and A3, we obtain the parity data (Ap) that arrives at 11101000.

Let's say one of the disks in the array (for example, Disk 2) fails. We can perform an A1 XOR A3 operation to get 00100010 as the output. If we perform another XOR operation with this output and the parity data, we get the following output:

(Video) Why You Should NOT Use RAID 5 Storage ( But Use RAID 6! )


With that, we've reconstructed the first byte of data on Disk 2. And that, in a nutshell, is how data parity provides fault tolerance and protects your data in the event of a drive failure. However, this redundancy has its limits, as RAID 5 only protects against drive failure. If two drives fail simultaneously, all data will be lost.

Finally, there is also the question of the layout of the data in the matrix. Unlike RAID levels 2, 3, and 4, which use a dedicated parity disk, RAID 5 uses split parity. This means that the parity blocks are distributed across the array instead of being stored on a single drive.

Our example above shows a left-to-right asynchronous layout, but this can change depending on certain factors. For example, blocks of data can be written from left to right or from right to left in the array. Consequently, the even block can be located at the beginning or at the end of the track.

In the case of a synchronous design, the location of the parity block also determines where the next distribution will start. For example, the following array is configured as left-synchronous, which means that data is written from left to right. Also, the parity block (Ap) determines where the next track (B1) starts, and so on.

What is RAID 5? How does it work (3)

Should I use RAID 5?

What is RAID 5? How does it work (4)

RAID 5 provides performance gains through striping and fault tolerance through parity. And unlike lower RAID levels, you don't have to deal with the bottleneck of a dedicated parity disk. This made it very popular in the 2000s, particularly in production environments.

However, RAID 5 has always had a critical flaw in that it only protects against asingle disk failure. In theory, two drives failing in succession are extremely unlikely. But during real world applications, things are different.

For starters, HDD sizes have grown exponentially, while read/write speeds haven't improved much. Because of this disparity, when a drive fails, rebuilding the array takes a long time. Depending on the size and specifications of the array, this can range from hours to days.

(Video) RAID 5 & RAID 6 - All You Need to Know as Fast As Possible

What is RAID 5? How does it work (5)

So people often buy discs in games. When you expose the same manufacturing units to the same workload and environment, the chances of them failing at the same time increase.

But let's say only one disk has failed. If you tend to rub your drive regularly, that's probably a good thing. But if you don't check for errors, there is a risk of running into ERU during the rebuild process, since one of the disks in the array has failed.

Unrecoverable read errors (UREs) are a major problem when rebuilding arrays because a single MB of unreadable data can render the entire array unusable. This is due to the way most RAID setups work.

Certain RAID implementations, such as ZFS RAID and Linux software RAID and some hardware drivers, mark the sector as bad and continue to rebuild. However, most hardware RAID controllers simply stop the rebuild and mark the entire array as failed.

The reasoning for this is that it is better to break the array rather than risk data corruption. This is done on the assumption that yourestore from a backupo recover data from each disk individually.

What is RAID 5? How does it work (6)

When you combine all of these factors, it's not hard to see why RAID 5 has fallen out of favor in recent years. This is why other versions of RAID, such as RAID 6 or ZFS RAID-Z2, are currently preferred, especially for larger arrays where rebuild times are longer and there is a chance of losing more data.

This is not to say that RAID 5 is irrelevant anymore. HDD manufacturers have taken this into account and improved the drives, exponentially reducing ERU occurrence rates in recent years. We recommend that you generally opt for other RAID levels, but if you want to use RAID 5 anyway, do so only for small size arrays.

Finally, here are some requirements and things worth knowing if you plan to set up a RAID 5 array:

(Video) What is RAID 0, 1, 5, & 10?

  • As mentioned above, a RAID 5 array requires a minimum of 3 drives. This is because at least 2 drives are required for striping and one more disk space is required to store parity data.
  • Usable storage in a RAID 5 configuration can be calculated as (N – 1) x (smallest disk size). You should use drives of the same size because if you use a mismatched configuration, the smaller drive will create a significant bottleneck.
  • RAID 5 offers excellent read performance as striping allows data to be read from multiple disks at the same time. However, at the same time, the write performance is not as good as the parity information for multiple disks must also be written.
  • RAID 5 can be configured through software implementations, but it is best to use hardware RAID controllers for a RAID 5 array, as performance is affected by software implementations.
  • Finally, RAID redundancy is not the same as backups. The purpose of RAID is simply to protect against drive failure. There are many reasons forhave independent off-site backups, from malware to human error and accidents.


How many drives do I need for RAID 5? ›

RAID 5 provides fault tolerance and increased read performance. At least three drives are required.

Why does RAID 5 need 3 disks? ›

The RAID 5 array contains at least 3 drives and uses the concept of redundancy or parity to protect data without sacrificing performance. Similar to a RAID 0 array which stripes data across multiple drives to improve performance, RAID 5 stripes data but adds an additional stripe of data known as parity for protection.

What is the difference between RAID 1 and RAID 5? ›

Raid 1 can tolerate more than 1 disk failure, while Raid 5 allows fault tolerance of only 1 disk. Raid 1 has slow write speeds when compared with Raid 5. The parity disk is not used in Raid 1, while Parity information is used well in Raid 5. Data loss cannot be managed and unacceptable in Raid 1.

What are the disadvantages of RAID 5? ›

Disadvantages of RAID 5
  • Longer rebuild time.
  • Uses half of the storage capacity (due to parity).
  • If more than one disk fails, data is lost.
  • More complex to implement.
Jul 23, 2019

Can two drives fail in RAID 5? ›

If a second disk in a RAID 5 disk array fails, the array also fails and its data is not accessible. If a second disk in a RAID level 5 disk array fails, you must replace the failed disks, then delete and recreate the disk array.

What happens if a disk fails in RAID 5? ›

When a single disk in a RAID 5 disk array fails, the disk array status changes to Degraded. The disk array remains functional because the data on the failed disk can be rebuilt using parity and data on the remaining disks. If a hot-spare disk is available, the controller can rebuild the data on the disk automatically.

How many drives can you lose in a RAID 5 before failure? ›

The downside to RAID 5 is that it can only withstand one disk drive failure. Thankfully, RAID 5 is hot-swappable, meaning one disk drive can be replaced while the others in the array remain fully functional.

Which level of RAID is best Why? ›

RAID 0 offers the best performance and capacity but no fault tolerance. Conversely, RAID 1 offers fault tolerance but does not offer any capacity of performance benefits. While performance is an important factor, backup admins may prioritize fault tolerance to better protect data.

Can you use different size hard drives in RAID 5? ›

Must hard drives in a RAID array be identical? No. It is perfectly valid to use hard drives from different manufacturers, model numbers, sizes, and rotational speed (spindle speed or RPM).

When should you not use RAID 5? ›

Dell recommends not using RAID 5 for any business-critical data. RAID 5 carries higher risks of encountering an uncorrectable drive error during a rebuild, and therefore does not offer optimal data protection.

What is RAID 5 best for? ›

RAID 5 is one of the most common RAID configurations and is ideal for application and file servers with a limited number of drives. Considered a good all-around RAID system, RAID 5 combines the better elements of efficiency and performance among the different RAID configurations.

Is RAID 5 still useful? ›

RAID level 5 offers a good compromise between cost and performance optimization compared to separate hard drives. The network also scores high for reliability. However, the reduced write rate means the storage solution is of little interest for databases with multiple larger files.

Which RAID is safest? ›

RAID 10 is the safest of all choices, it is fast and safe. The obvious downsides are that RAID 10 has less storage capacity from the same disks and is more costly on the basis of capacity. It must be mentioned that RAID 10 can only utilize an even number of disks as disks are added in pairs.

Is RAID 5 good for home use? ›

RAID 5 gets a lot of flak these days. You either run RAID 1, RAID 10 or you use RAID 6, but if you run RAID 5 you're told that you are a crazy person. Using RAID 5 is portrayed as an unreasonable risk to the availability of your data.

What is the most reliable RAID level? ›

RAID 5 utilizes parity data on all the storage drives to retrieve lost data. Although writing data onto the drives is much slower, it can be read fast. Most people would say that RAID 5 is the most reliable level because data is retrievable without jeopardizing the performance of the system.

Can you mix SSD and HDD in RAID 5? ›

Even though it's possible to set up a RAID with SSD and HDD, the outcome will be an array performing only as fast as the slowest drive. Mixing RAID with SSD and HDD will lower the bar if you consider any RAID configuration, whether striping, mirroring, or parity, simply because an HDD can do only so much.

What is the best RAID for two drives? ›

RAID 1 Arrays

A RAID 1 array is built from two disk drives, where one disk drive is a mirror of the other (the same data is stored on each disk drive). Compared to independent disk drives, RAID 1 arrays provide improved performance, with twice the read rate and an equal write rate of single disks.

How does RAID 5 recover data? ›

Once the data is found and RAID parameters are set, RAID 5 data can be recovered using automated RAID recovery software or through manual recovery means. The manual RAID 5 recovery process requires the user to find the parity position and rotation of the storage array.

Does RAID 5 slow down performance? ›

RAID 5 arrays have relatively slow write performance because parity information must be written to the disks alongside the actual data. RAID 6 arrays are even slower because they store a greater volume of parity data than RAID 5 arrays do.

How long do RAID drives last? ›

The simplest answer is that they can run smoothly for three to five years. This means any HDD, whether it's external or inside of a system. Asking about the longevity of an external enclosure—a metal or plastic housing designed to cover and protect a disk drive from damage—is a different question altogether.

How long should it take for a RAID 5 disk to rebuild? ›

RAID Disk Failure Calculator from Memset
Disk Size (GB)Rebuild Timeraid5 with 3 hotspares
50013 hours, 53 minutes10
10001 day, 3 hours20
20002 days, 7 hours40
1 more row

Which RAID is best for speed? ›

RAID 0 is the only RAID type without fault tolerance. It is also by far the fastest RAID type. RAID 0 works by using striping, which disperses system data blocks across several different disks.

Why RAID 6 is better than RAID 5? ›

In general, a RAID 6 configuration offers better data protection and fault tolerance than RAID 5. However, RAID 6 dual parity requires more time to rebuild lost data as it will be using parity data from two different storage drives.

What is an advantage of RAID 5 over RAID 1? ›

RAID 5. RAID 1 is a simple mirror configuration where two (or more) physical disks store the same data, thereby providing redundancy and fault tolerance. RAID 5 also offers fault tolerance but distributes data by striping it across multiple disks.

What is RAID for dummies? ›

RAID (redundant array of independent disks) is a way of storing the same data in different places on multiple hard disks or solid-state drives (SSDs) to protect data in the case of a drive failure. There are different RAID levels, however, and not all have the goal of providing redundancy.

What RAID is best for SSD? ›

RAID 4. This is the preferred configuration for SSD RAIDs by storing all parity data on a single SSD. This provides the fastest performance with the greatest capacity while still protecting you if an SSD dies.

Is there anything better than RAID? ›

Object storage offers a far simpler and more flexible alternative to RAID and block storage. A unique ID is assigned to each object when it is created. The object can be stored on a local server or in a cloud-based data center halfway around the world.

Can RAID disk be cloned? ›

For Windows Operating System, the RAID array virtual drives are the same as the physical drive after building the RAID array. That's to say, you can clone RAID drive as a physical disk.

Do you need a RAID controller for RAID 5? ›

For RAID 5 or 6, you will most certainly need a dedicated hardware controller. This is due to the need to calculate the parity data and write it across all the disks.

How much space do you lose on RAID 5? ›

RAID 5 results in the loss of storage capacity equivalent to the capacity of one hard drive from the volume. For example, three 500GB hard drives added together comprise 1500GB (or roughly about 1.5 terabytes) of storage.

How do I know which RAID to use? ›

To check RAID type from the command line:
  1. Go to System Settings.
  2. Click CLI Console.
  3. Type the command diagnose system raid status and press Enter.
  4. The following information is shown in the output: Mega RAID - this output shows that the device uses hardware RAID.

How do I know if RAID 5 is working? ›

To view the RAID status, go to System Settings > RAID Management. The RAID Management pane displays the RAID level, status, and disk space usage. It also shows the status, size, and model of each disk in the RAID array.

Which RAID is best for large drives? ›

RAID 0 is great for professionals looking for large volumes, increased speed, and can afford to work with no concern for data loss. For instance: a video editor who copies files from multiple sources or servers onto a large work drive. With RAID 0, all hard drives are striped together.

Why is RAID 10 better than 5? ›

RAID 10 provides excellent fault tolerance — much better than RAID 5 — because of the 100% redundancy built into its designed. In the example above, Disk 1 and Disk 2 can both fail and data would still be recoverable. All disks inside a RAID 1 group of a RAID 10 setup would have to fail for there to be data loss.

Which RAID is best for 10 disks? ›

RAID 10 offers very good performance with good data protection and no parity calculations. RAID 10 requires a minimum of four drives, and usable capacity is 50% of available drives. It should be noted, however, that RAID 10 can use more than four drives in multiples of two.

What are the disadvantages of RAID? ›

Overview of the pros and cons of RAID 0
Advantages of RAID 0Disadvantages of RAID 0
Higher number of input and output operations per second compared to single drives (HDD)A lack of redundancy means data may be lost in the event of a defective disk
1 more row
Jan 10, 2023

Which RAID is most redundant? ›

RAID-10 has the best performance and redundancy characteristics but halves the usable capacity, which can make it expensive to deploy at scale. Sometimes this will be referred to as RAID-1, even though technically RAID-1 refers to only two disks.

What do you need for RAID 5? ›

At least three drives are required for RAID 5. No matter how many drives are used, an amount equal to one of them will be used for the recovery data and cannot be used for user data. You can lose any one disk and not lose your backup data. Just replace the disk with a new one.

How many disks for RAID 5 best practices? ›

With RAID 5, the ideal number of drives is one more than a power of 2, so 5 drives is one of the optimum sizes. This allows the implementation to make both the block size and the stripe size powers of two.

What are Level 7 raids? ›

RAID 7 is a type of RAID level that includes a real-time embedded operating system and processor for enhanced data read/write or I/O operations and data caching capabilities. It is a propriety RAID level owned by Storage Computer Corporation.

How long does a Tier 5 RAID last? ›

For all Tier 1 – 4 raids the raid timer is 180 seconds long. Tier 5 timer is 300 seconds long.

What is the best RAID configuration for 5 drives? ›

RAID 5 (Striping with Parity)

As the most common and best “all-round” RAID level, RAID 5 stripes data blocks across all drives in an array (at least 3 to a maximum of 32), and also distributes parity data across all drives (Figure 5).

Is RAID 5 faster with more drives? ›

RAID 5 helps to increase operation speed by using multiple drives throughput to write blocks of information. This means a single file or program can be distributed across a minimum of three hard drives quickly. The benefit is increased data read/write speeds which speeds up project time and overall performance.

How to calculate RAID 5? ›

A simple rule for RAID 5 calculation is to take the amount of capacity on the disk drive (in this case 146 GB) and reduce it by about 15% to get an idea of the usable amount that will be available to hosts.

Which RAID requires at least 4 drives? ›

RAID 10, also known as RAID 1+0, is a RAID configuration that combines disk mirroring and disk striping to protect data. It requires a minimum of four disks and stripes data across mirrored pairs. As long as one disk in each mirrored pair is functional, data can be retrieved.

How many drives can fail in RAID 5? ›

The downside to RAID 5 is that it can only withstand one disk drive failure. Thankfully, RAID 5 is hot-swappable, meaning one disk drive can be replaced while the others in the array remain fully functional.

What type of RAID is best? ›

RAID 10 is a combination of RAID 1 and 0 and is often denoted as RAID 1+0. It combines the mirroring of RAID 1 with the striping of RAID 0. It's the RAID level that gives the best performance, but it is also costly, requiring twice as many disks as other RAID levels, for a minimum of four.

Which level of RAID is best why? ›

RAID 0 offers the best performance and capacity but no fault tolerance. Conversely, RAID 1 offers fault tolerance but does not offer any capacity of performance benefits. While performance is an important factor, backup admins may prioritize fault tolerance to better protect data.

What percentage does RAID 5 lose? ›

RAID 5 loses 33 percent of storage space (using three drives) for that parity, but it is still a more cost-effective setup than RAID 1. The most popular RAID 5 configurations use four drives, which lowers the lost storage space to 25 percent. It can work with up to 16 drives.

What are the benefits of RAID 5? ›

RAID 5 protection protects against a one disk unit failure. If more than one disk fails, you must restore the data from the backup media. Logically, the capacity of one disk unit is dedicated to storing parity data in a parity set. However, in practice the parity data is spread across the disk units.

Can you do RAID 5 with different size drives? ›

Must hard drives in a RAID array be identical? No. It is perfectly valid to use hard drives from different manufacturers, model numbers, sizes, and rotational speed (spindle speed or RPM).

What RAID is most secure? ›

RAID 5 is the most common secure RAID level. It requires at least 3 drives but can work with up to 16. Data blocks are striped across the drives and on one drive a parity checksum of all the block data is written.

Why is RAID 5 preferred to RAID 4? ›

With respect to performance, RAID 5 will generally outperform RAID 4. With RAID 4, you have a dedicated parity drive, which means that the parity drive will be a bottleneck in high I/O situations. RAID 5, however, spreads not only the data but also the parity information across all drives in the RAID set.

What is the most common RAID? ›

The most common types are RAID 0 (striping), RAID 1 (mirroring) and its variants, RAID 5 (distributed parity), and RAID 6 (dual parity). Multiple RAID levels can also be combined or nested, for instance RAID 10 (striping of mirrors) or RAID 01 (mirroring stripe sets).


1. What is a RAID Array, RAID 0, 1, 5, 10. Advantages and Disadvantages of RAID 0. 1. 5 10
2. Raid Parity Bits explained- How they work
(Jacob Dykstra)
3. What is RAID? RAID 0, RAID 1, RAID 4, RAID 5, RAID 6, Nested RAID 10 Explained
(Gate Smashers)
4. RAID 0, RAID 1, RAID 10 - All You Need to Know as Fast As Possible
5. How RAID Works
(Dave's Garage)
6. EASY GUIDE to RAID 0, 1, 4, 5, 6, 10 // Featuring the Synology DS1019+ NAS
(Sidney Diongzon)


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