RAID 5 vs RAID 6: Differences, Benefits and Disadvantages

Updated July 16, 2019

Table of Contents

What is RAID 5 vs RAID 6?

RAID 5 and RAID 6 uses striping with distributed parity technique. However, in comparing RAID 5 vs RAID 6, while RAID 5 uses a single independent parity scheme, RAID 6 uses two independent parity schemes.

This guide provides a simplified but comprehensive comparison of these two RAID types. It also explores the advantages and disadvantages of each RAID level.

To be able to compare RAID 5 vs RAID 6, I will first explain how each RAID type works. I will also discuss their advantages and disadvantages. Finally, I will draw a comprehensive comparison between RAID 5 and RAID6.

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RAID 5 Explained

The diagram below is an illustration of RAID 5. All discussions in this section will reference this diagram.

RAID 5 splits data into blocks of certain “block size” and distributes them across all the disks in the array. Apart from splitting data into blocks, RAID 5 also creates parity information using a checksum method. Parity information is also distributed across all the disks that make up the array.

In the diagram above, block 1a, 1b and 1c represents a data block distributed across the 3 disks. Notice that on the 4th disk, instead of creating a 4th data block, a parity information, parity p1 is created on the data block array.

RAID 5 requires a minimum of 3 disks to create an array. In theory you can add as many disks as you want. But in practice the RAID controller will have a maximum capacity it can handle. So, the maximum number of drive will vary from one controller to another.

RAID 6 Explained

The diagram below is a visual representation of RAID 6.

Like RAID 5, RAID 6 also splits data into blocks and distributes the blocks across the disks in the array. It also creates and splits parity information across all disks.

However, one difference between RAID 5 vs RAID 6 is the number of parity functions. In a RAID 5 array, a single parity function is calculated. But in RAID 6, two separate parity functions are used.

Typically, the first parity function in a RAID 6 array is similar to what is available in a RAID 5 array. But in a RAID 6 the second parity function is more complex.

As you will see later in this guide, while a RAID 5 can only recover from a single drive failure a RAID 6 can recover from 2 simultaneous drive failures. For this reason while RAID 5 requires a minimum of 3 disks RAID 6 needs at least 4 disks.

In the next section, I will provide a comprehensive but simplified comparison of RAID 5 vs RAID 6. The section will compare different features of both RAID levels.

RAID 5 vs RAID 6 Compared

So far this guide have explained RAID 5 and RAID 6. The basic similarity between the two RAID levels is that both offer striping with distributed parity. But while RAID 5 uses a single parity function, RAID 6 uses 2 separate independent parity functions.

This section compares RAID 5 vs RAID 6. It compares the following features: Number of disks, soft vs hardware RAID, Available disks for data, Cost of Implementation, Performance and Recovery.

RAID 5 or RAID 6: Disks Requirements and Space Availability

As I already stated in this guide, you require a minimum of 3 disks to create a RAID 5 array. On the other hand, a RAID 6 array requires a minimum of 4 disks.

However, both offers differences in disk storage availability. The capacity of a RAID 5 array is (N-1), multiplied by the size of the smallest disk in the array. As an example, for a RAID 5 array with 4, 512 GB drives. The total capacity of the array will be:

(4-1)*512 GB = 1536 GB (1.536 TB)

In a RAID 5 array you lose one hard drive.

For a RAID 6 array, the capacity of the array is (N-2) times the size of the smallest disk. Continuing with the previous example, a RAID 6 array with 4, 512 GB disks available capacity will be:

 (4-2)*512 GB = 1024 GB (1 TB)

While you lose 1 disk in a RAID 5, for a RAID 6 you lose 2 disks.

For the illustration in this section N represents the number of disks in a RAID array. GB is Gigabyte while TB is Terabyte.

RAID 5 or RAID 6: Soft vs Hardware RAID

A software RAID does not require a RAID hardware but a hardware RAID does. In comparing RAID 5 vs RAID 6, you can configure both soft and hardware RAID 5 but to create a RAID 6 array, you require a RAID hardware.

RAID 5 or RAID 6: Cost of Implementation

Based on the last two compared features, compared to RAID 5 a RAID 6 array requires one more disk and provides half the capacity of all available disks. RAID 6 also requires a RAID card (hardware). All these add to the cost of implementation compared to RAID 5.

However, as you will see in the next sections, the additional costs of implementing RAID 6 comes with some added benefits especially in relation to disk redundancy and data recovery.

RAID 5 or RAID 6: Performance

The read performance of a RAID 5 array is very close to that of a RAID 6. However, write performance of a RAID 6 array is slightly slower due to the additional parity information that needs to be calculated.

This means that, if implemented with the same number and types of disks a RAID 6 array may be marginally slower than a RAID 5 array.

Having said that a RAID 6 array provides one major recovery benefit. That is the ability to recover in the event of 2 simultaneous disk failures. This may far outweigh the marginal drop in performance due to the complexity of parity information computation.

RAID 5 vs RAID 6: Recovery

As I already stated earlier in this guide you can recover a RAID 5 array if 1 disk fails. But if 2 disks fails simultaneously, recover may be impossible. This means that you may experience a data loss.

However, a RAID 6 array can recover from 2 simultaneous disk failures. This is one benefit of using a RAID 6 instead of a RAID 5 array.

Conclusion

This guide compared RAID 5 vs RAID 6. Both are implemented using striping with distributed parity. However, while RAID 5 uses 1 parity function, RAID 6 uses 2.

The implication is that you can recover a RAID 6 array with 2 simultaneous disk failures. But a RAID 5 array can only recover from one disk failure.

In terms of Read performance, RAID 5 and RAID 6 offers the same benefits. However, for Write, RAID 6 may be marginally slower. This is due to the additional parity calculation requirement.

I hope this has been insightful. Have any question or comment? Use the “Leave a Reply” form at the end of the page. You may also share your experience so other readers can benefit from it.