RAID Configurations for CompTIA A+ 220-1101

RAID 0 stripes data across two or more drives in alternating chunks. No redundancy — if one drive fails, all data is lost. Performance: excellent read AND write performance (data is read from multiple drives simultaneously). Effective capacity: total capacity of all drives combined (2×1TB = 2TB usable). Minimum drives: 2. Use case: performance-critical applications where data loss is acceptable (video editing scratch disks, gaming). Identifying characteristic: 'striped' disk set, no fault tolerance. If 4 drives are used: 4× read performance, 4× write performance, 0 fault tolerance. Not recommended for any data that matters — one drive failure destroys all data.

RAID 1 mirrors data identically across two drives simultaneously. Full redundancy — if one drive fails, the other contains an exact copy. Read performance: slightly improved (can read from either drive). Write performance: same as single drive (must write to both). Effective capacity: 50% of total capacity (2×1TB = 1TB usable). Minimum drives: 2. Can survive loss of one drive. Use case: OS drives, critical data where simplicity and reliability matter more than capacity. Identifying characteristic: 'mirrored' disk set, excellent fault tolerance. Rebuild: replace failed drive, RAID controller mirrors surviving drive to new drive (rebuild time proportional to drive size).

RAID 5 stripes data and parity information across three or more drives. Parity is distributed — not on a dedicated parity drive. Can survive loss of ONE drive. Read performance: excellent (data spread across multiple drives). Write performance: slower than RAID 0 (parity calculation overhead). Effective capacity: (N-1) drives worth of data. 3×1TB = 2TB usable. 4×1TB = 3TB usable. Minimum drives: 3. Use case: balance of performance, redundancy, and capacity — the most common RAID for small servers and NAS devices. Rebuild risk: during rebuild (after one drive fails), a second drive failure destroys all data. Large drives = long rebuild time = high risk window. RAID 6 adds a second parity (can survive 2 drive failures) at minimum 4 drives.

RAID 10 combines RAID 1 (mirroring) and RAID 0 (striping). Minimum drives: 4 (in pairs). Each pair is mirrored (RAID 1), and the mirrored pairs are striped (RAID 0). Effective capacity: 50% of total capacity. 4×1TB = 2TB usable. Can survive loss of one drive per mirrored pair — potentially multiple drive failures if they are in different pairs. Read and write performance: excellent (combines striping speed with mirroring reliability). Use case: high-performance databases, critical servers requiring both speed and redundancy. Most expensive RAID level in terms of drive cost per usable TB.

Hardware RAID: dedicated RAID controller card (or built into server motherboard). Controller manages all RAID functions independently of the OS. Benefits: better performance (dedicated processor), OS-agnostic (drive array appears as single disk to OS), hot-swap support, battery-backed cache. Cost: RAID controllers can be expensive. Software RAID: managed by the OS. Windows: Disk Management or Storage Spaces. Linux: mdadm. Benefits: no additional hardware cost. Drawbacks: uses CPU resources, varies in feature support by OS. Fake RAID (HostRAID): RAID managed by the motherboard BIOS/driver — not true hardware RAID, not true software RAID. Usually inferior to both. Hot spare: a standby drive automatically added to rebuild a failed drive without manual intervention.

RAID comparison table: RAID 0: minimum 2 drives, 0 fault tolerance, full capacity, best performance. RAID 1: minimum 2 drives, 1 drive fault tolerance, 50% capacity, good read, normal write. RAID 5: minimum 3 drives, 1 drive fault tolerance, (N-1)/N capacity, good read, moderate write. RAID 10: minimum 4 drives, 1 per pair fault tolerance, 50% capacity, best performance, best redundancy. Key A+ exam rule: RAID is NOT a backup. RAID protects against drive hardware failure but not: accidental deletion, ransomware, software corruption, fire/flood. Always combine RAID with a backup strategy.