RAID

What is RAID?

RAID is a technology for virtualizing data storage that combines multiple individual drives to enhance storage performance and reliability. Server RAID can boost data throughput by utilizing more drives for storing and accessing data. The use of multiple drives also ensures data redundancy, enhancing the operating system's fault tolerance.

Types of RAID

Server RAID aims to achieve performance, reliability, availability, and capacity. Each RAID level represents a distinct configuration that addresses these objectives differently.

RAID 0

RAID 0 utilizes disk striping to enhance server performance without disk mirroring or parity. It improves input and output performance by distributing data read and write operations across multiple disks simultaneously. RAID 0 aggregates the storage capacities of all drives, maximizing storage capacity utilization. However, RAID 0 lacks data redundancy and fault tolerance. A single drive failure can compromise the entire array, potentially leading to data loss or corruption. Therefore, RAID 0 is suitable primarily for non-critical storage applications, such as temporary file backups.

RAID 1

RAID 1 employs disk mirroring to duplicate data across two or more disks, ensuring maximum redundancy. Any read request can be fulfilled by any drive, allowing continuous operation even if one drive fails. RAID 1 also enhances read performance but requires writing the same data to multiple disks, reducing usable capacity. It is ideal for small databases or applications needing full data redundancy despite lower storage capacity utilization.

RAID 5

RAID 5 employs block-level striping with distributed parity, where parity information is spread across the drives. In case of a drive failure, the parity data can reconstruct user data, making it highly reliable for fault tolerance. However, the computational load during extensive data reads can impact server performance, leading to latency. Moreover, replacing and restoring data after a drive failure can be time-consuming.

In summary, RAID 5 remains the most prevalent and secure RAID level due to its robust performance and ample storage capacity.

RAID 6

RAID 6 is akin to RAID 5 but employs striping with double parity. If one drive fails, the controller uses one set of parity data to rebuild the data. Should another drive fail before the array is restored, the remaining data and two sets of parity can reconstruct the contents of the two missing drives. Thus, RAID 6 offers protection against dual-disk failures, enhancing its practicality.

Compared to RAID 5, RAID 6 delivers increased redundancy and read performance. However, during intensive write operations, it may experience a similar performance reduction due to dual parity calculations.

RAID 10

RAID 10 combines RAID 1 and RAID 0, striping data across disks to enhance data transfer speed while ensuring complete redundancy through data mirroring. This configuration necessitates at least two mirror sets working in tandem, where multiple RAID 1 sets unite to form a single array.

By eliminating parity-related delays, RAID 10 enables rapid rebuilds in case of failures, making it the fastest option in such scenarios. However, it remains the most costly among RAID configurations.

Other server RAID levels are derived from the primary RAID configurations mentioned earlier and are tailored for specific use cases.

RAID 2

RAID 2 utilizes bit-level striping with dedicated Hamming-code parity. It is no longer used in commercially available systems due to high implementation costs and poor performance in specific disk I/O operations.

RAID 3

RAID 3 employs byte-level striping with dedicated parity, where parity is computed for corresponding bytes and stored on a dedicated parity drive. Like RAID 2, it is also infrequently used in practical applications.

RAID 4

RAID 4 utilizes block-level striping across multiple disks with dedicated parity. In RAID 4, all parity information is written to a single disk, which can lead to slower write performance. RAID 5 addresses this issue, making it more commonly adopted compared to RAID 4.

Pros, Cons, and Usage of RAID Levels

There are notable distinctions among various RAID types. Users should understand the pros, cons, and optimal applications of each RAID configuration to select the most suitable one. The table below provides detailed answers.