RAID: Using Multiple Disks for Performance and Redundancy

Understanding RAID Technology

RAID technology enables the consolidation of several physical hard drives into one unified logical drive. This process facilitates data mirroring across multiple drives, providing enhanced data security.

By storing information in multiple locations, RAID ensures that critical data remains accessible even if one drive fails.

What Does RAID Stand For?

The acronym RAID originally signified "redundant array of independent disks." However, it’s important to note that certain RAID configurations prioritize performance gains over data redundancy.

These performance-focused RAID levels do not offer the same level of data protection as those designed for redundancy.

Key Benefits of RAID

• Data Redundancy: Protects against data loss due to drive failure.
• Improved Performance: Certain RAID levels can significantly boost read and write speeds.
• Increased Storage Capacity: Combines the storage space of multiple drives.

The specific benefits realized depend on the chosen RAID level and its configuration.

Selecting the appropriate RAID setup is crucial for balancing performance, redundancy, and storage capacity needs.

RAID Levels

RAID encompasses a variety of methods for combining multiple disks. Different RAID levels deliver varying degrees of performance and data protection. A common characteristic across all RAID levels is the consolidation of several physical disks into a single logical unit, as presented to the operating system.

Understanding RAID Configurations

• RAID 0: Unlike its counterparts, RAID 0 does not incorporate redundancy. Its primary benefit lies in enhanced performance through disk aggregation. Data written by the computer is distributed evenly across two or more hard drives. For instance, a 100MB file might be split into 50MB segments written to each of two drives. Simultaneous reading from multiple drives accelerates data retrieval compared to a single drive. However, the failure of any drive within the RAID 0 array results in complete data loss. Multiple disks appear as a single, faster unit, but with increased vulnerability.
• RAID 1: RAID 1 employs disk mirroring for data security. When 100MB of data is written, it's duplicated identically onto both hard disks. This ensures a complete, current data copy exists on each drive. Consequently, a disk failure doesn't lead to data loss, as the remaining disk holds a full backup.
• RAID 2, 3, and 4: These RAID levels are infrequently utilized and are largely considered outdated in modern storage systems.
• RAID 5: Implementing RAID 5 requires a minimum of three disks. It utilizes striping to distribute data across all drives, coupled with parity data also spread across all disks. Should a drive fail, data integrity is maintained. RAID 5 offers redundancy at a lower storage cost than RAID 1; for example, four 1TB drives could form two 1TB RAID 1 arrays (totaling 2TB) or a single 3TB RAID 5 array.
• RAID 6: Similar to RAID 5, RAID 6 enhances data protection by adding a second parity block. This means two parity blocks are written for each data segment distributed across the disks. While reducing usable storage capacity, RAID 6 provides greater resilience against data loss. Unlike RAID 5, where two drive failures cause data loss, RAID 6 can withstand the failure of two drives without compromising data.
• RAID 10: Often referred to as RAID 1+0, RAID 10 combines striping and mirroring. Data is first divided across primary disks and then mirrored onto secondary disks. This configuration aims to leverage the performance benefits of RAID 0 with the redundancy of RAID 1.

Beyond these standard levels, various non-standard RAID configurations also exist.

The choice of RAID level depends on the specific needs of the system, balancing performance, redundancy, and cost.