RAID 5 Explained

5 min readJun 7, 2023

Photo by PITS Global Data Recovery Services

The need to protect valuable information against hardware failures and data loss has led to the development of various RAID (Redundant Array of Independent Disks) configurations. Among these, RAID 5 stands out as a popular choice due to its efficient balance between performance, reliability, and cost-effectiveness.

In this blog, we will talk about what RAID 5 is and how it functions as a robust data storage solution.

What is RAID 5?

RAID 5 is a data storage technology that uses multiple drives to achieve fault tolerance and data redundancy. It requires a minimum of three disks to implement, although it can work with more disks as well. Unlike other RAID levels, RAID 5 distributes protection information across all the drives in the array, which helps maintain data integrity in the event of a drive failure.

Structure

A RAID 5 array is composed of multiple disks, typically three or more. The data is divided into blocks and striped across all the drives in the array, with each drive storing a portion of every block. Alongside the data blocks, RAID 5 also calculates parity information, which is distributed across the drives. This distributed parity scheme ensures that no single drive holds all the parity information. Instead, each drive in the array stores a portion of the parity data. This distribution enhances the array’s fault tolerance, as the failure of any single drive can be recovered by using the parity information distributed across the remaining drives.

Space Efficiency

One of the advantages of RAID 5 is its space efficiency. By distributing parity information across the drives, RAID 5 allows for efficient use of disk space.

The total usable capacity of a RAID 5 array is the sum of the capacities of all the drives in the array, subtract the capacity of one drive, which is reserved for parity information.

U = (N — 1) * S

U — Usable capacity
N — Number of disks
S — Size of the smallest disk

For example, in a RAID 5 array with four 1 TB drives, the usable capacity would be 3 TB.

Redundancy and Fault Tolerance

RAID 5 provides fault tolerance by using parity data. If one drive in the array fails, the parity information stored on the remaining drives can be used to reconstruct the missing data. The array continues to function in a degraded state until the failed drive is replaced and rebuilt. The parity information, distributed across the remaining drives, allows for the reconstruction of the failed drive’s data.

The distributed parity scheme also offers protection against data loss in the case of a single drive failure. This redundancy ensures that even if one drive fails, the data stored in the array remains intact and accessible. However, it’s important to note that if multiple drives fail or if a failed drive is not promptly replaced, there is a risk of data loss. Therefore, it is crucial to monitor the health of the drives and replace any failed ones as soon as possible.

Performance and Capacity

RAID 5 offers a good balance between performance and capacity. Since the data is striped across multiple drives, read and write operations can be performed concurrently, resulting in improved performance. The array’s capacity, as we’ve mentioned earlier, is determined by the total capacity of all the drives minus one drive reserved for parity. As a result, RAID 5 provides efficient capacity utilization, allowing for larger usable storage compared to other RAID levels, such as RAID 1 (mirroring). However, write operations require additional processing time to calculate and write parity information, which introduces the write penalty.

Write Penalty and Rebuild Time

The write penalty refers to the additional time required to calculate and write parity information during write operations. This can affect the overall write performance of a RAID 5 array compared to a RAID level without parity, such as RAID 0. The write penalty is most noticeable during random write operations since each write operation requires updating the corresponding data block and the associated parity information. However, the impact of the write penalty can be mitigated by using a dedicated hardware RAID controller or by employing newer software implementations that optimize the write process.

Rebuilding a failed drive in a RAID 5 array can take time, especially for larger capacity drives. During the rebuild process, the data from the remaining drives and the parity information are used to reconstruct the missing data on the new drive. The rebuild time depends on factors such as the size of the drives, the load on the array during the rebuild, and the performance of the system. It’s important to note that during the rebuild process, the array is in a vulnerable state, as any additional drive failure can lead to data loss. Therefore, it is important to have a backup strategy in place and to monitor the rebuild process closely to ensure data integrity and availability.

Pros of RAID 5

Offers a good balance of performance and data redundancy.
Efficient use of storage capacity, as parity is distributed across drives.
Can withstand the failure of a single drive without data loss.

Cons of RAID 5

Write performance can be impacted due to the need to calculate parity.
Rebuilding an array after a drive failure can be time-consuming and resource-intensive.
If multiple drives fail or develop bad sectors during the rebuild process, data loss may occur.

Conclusion

RAID 5 offers a compelling balance between storage efficiency, fault tolerance, and performance. It is widely adopted in various applications where a combination of data protection and capacity optimization is desired. By distributing data and parity information across multiple drives, RAID 5 provides redundancy and fault tolerance, safeguarding against drive failures. However, it’s important to carefully consider the rebuild time and the potential risk of multiple drive failures to ensure data integrity and availability. Implementing RAID 5, combined with proper monitoring and maintenance, can provide a reliable and efficient storage solution for a wide range of applications.