RAID 0, 1, 5, 6, 50: Key Differences and Use Cases

RAID 0, 1, 2, 5, 6 & RAID 50

A detailed technical overview of common RAID (Redundant Array of Independent Disks) levels, including their architectures, performance, fault tolerance, use cases, and tradeoffs:

1. RAID 0 (Striping)

Definition:

RAID 0 (also called “striping”) splits data evenly across two or more drives without parity or mirroring. It focuses solely on performance, using all drives in the array to read/write data in parallel.

Key Characteristics

Minimum Drives: 2
Data Distribution: Data is divided into “stripes” and distributed across all drives (e.g., Stripe 1 on Drive 1, Stripe 2 on Drive 2, Stripe 3 on Drive 1, etc.).
Fault Tolerance: None – if one drive fails, all data in the array is lost (no redundancy).
Capacity: 100% of total drive capacity (e.g., 2×1TB drives = 2TB usable space).
Performance:
- Read Speed: High (parallel reads across drives).
- Write Speed: High (parallel writes across drives).

Common Use Cases

High-performance workloads (video editing, 3D rendering, gaming).
Temporary data storage (no critical data).
Non-critical caching or scratch disks.

Pros & Cons

Pros	Cons
Maximum read/write performance	No fault tolerance (single drive failure = total data loss)
Full utilization of drive capacity	Not suitable for critical data
Simple implementation

2. RAID 1 (Mirroring)

Definition:

RAID 1 (also called “mirroring”) duplicates data across two or more drives, creating an exact copy (mirror) of all data on every drive in the array.

Key Characteristics

Minimum Drives: 2
Data Distribution: Identical data is written to all drives (e.g., Drive 1 and Drive 2 both store the same data).
Fault Tolerance: High – can survive the failure of all but one drive (e.g., 2-drive array survives 1 failure; 3-drive array survives 2 failures).
Capacity: 50% of total drive capacity (e.g., 2×1TB drives = 1TB usable space; 3×1TB drives = 1TB usable space).
Performance:
- Read Speed: Moderate to high (parallel reads from mirrored drives).
- Write Speed: Same as a single drive (data must be written to all drives).

Common Use Cases

Critical data storage (financial records, databases, server OS drives).
Systems requiring high uptime (file servers, email servers).
Small business or personal backups.

Pros & Cons

Pros	Cons
Excellent fault tolerance	50% capacity loss (high storage cost)
Fast rebuilds (simply copy data from surviving drive)	Lower write performance than RAID 0
Simple to implement and maintain

3. RAID 2 (Bit-Level Striping with Hamming Code)

Definition:

RAID 2 uses bit-level striping (data split into individual bits) across data drives, with dedicated parity drives using Hamming code for error correction. It is a legacy RAID level rarely used in modern systems.

Key Characteristics

Minimum Drives: 3 (data drives + parity drives; typically 4–8 drives total).
Data Distribution: Bits of data are striped across data drives; parity drives store Hamming code for error detection/correction.
Fault Tolerance: High – corrects single-bit errors and detects multi-bit errors (survives 1 drive failure).
Capacity: (Total capacity) – (parity drive capacity) (e.g., 4×1TB drives = 3TB usable space).
Performance:
- Read/Write Speed: High for large sequential data (bit-level parallelism), but inefficient for small random reads/writes.

Common Use Cases

Legacy mainframe systems (designed for early hard drives with high bit-error rates).
No modern consumer or enterprise use (superseded by RAID 3/5).

Pros & Cons

Pros	Cons
Advanced error correction for noisy drives	Obsolete (no modern hardware support)
High sequential performance	Inefficient for random access workloads
	Requires multiple dedicated parity drives (high cost)

4. RAID 5 (Block-Level Striping with Distributed Parity)

Definition:

RAID 5 uses block-level striping (data split into blocks) across three or more drives, with parity information distributed evenly across all drives (no dedicated parity drive).

Key Characteristics

Minimum Drives: 3
Data Distribution: Data blocks and parity blocks are interleaved across all drives (e.g., Drive 1: Data 1, Parity 2; Drive 2: Data 2, Parity 3; Drive 3: Data 3, Parity 1).
Fault Tolerance: Survives 1 drive failure (parity data rebuilds lost data from surviving drives).
Capacity: (Total capacity) – (1 drive capacity) (e.g., 3×1TB drives = 2TB usable space; 4×1TB drives = 3TB usable space).
Performance:
- Read Speed: High (parallel reads across all drives).
- Write Speed: Moderate (parity must be recalculated and written for every change).

Common Use Cases

Mid-sized file servers (document storage, media libraries).
Databases with mixed read/write workloads.
Enterprise storage for non-critical but important data.

Pros & Cons

Pros	Cons
Balances capacity, performance, and fault tolerance	Risk of data loss during rebuild (second drive failure = total loss)
More efficient capacity than RAID 1	Slow rebuilds (parity calculation is CPU-intensive)
No dedicated parity drive (better resource utilization)	Not recommended for large drives (rebuild time increases with drive size)

5. RAID 6 (Block-Level Striping with Double Distributed Parity)

Definition:

RAID 6 is an extension of RAID 5 with double distributed parity (two sets of parity data) across all drives, enabling survival of two simultaneous drive failures.

Key Characteristics

Minimum Drives: 4
Data Distribution: Data blocks and two sets of parity blocks are distributed across all drives.
Fault Tolerance: Survives 2 drive failures (e.g., 4-drive array survives 2 failures; 6-drive array survives 2 failures).
Capacity: (Total capacity) – (2 drive capacities) (e.g., 4×1TB drives = 2TB usable space; 6×1TB drives = 4TB usable space).
Performance:
- Read Speed: High (same as RAID 5, parallel reads across drives).
- Write Speed: Lower than RAID 5 (two parity blocks must be recalculated/written for every change).

Common Use Cases

Large-scale storage systems (data centers, cloud storage).
Critical databases or file servers with high uptime requirements.
Arrays using large-capacity drives (reduces rebuild risk).

Pros & Cons

Pros	Cons
Higher fault tolerance than RAID 5 (survives 2 drive failures)	Lower write performance than RAID 5
Safer for large drives (reduced rebuild failure risk)	2-drive capacity loss (higher storage cost than RAID 5)
Suitable for large-scale enterprise storage	More CPU-intensive (parity calculations for two sets of parity)

6. RAID 50 (RAID 5 + RAID 0, Striped RAID 5 Arrays)

Definition:

RAID 50 (also called “RAID 5+0”) is a nested RAID level that combines RAID 5 (parity) and RAID 0 (striping). It consists of multiple RAID 5 sub-arrays striped together to balance performance, capacity, and fault tolerance.

Key Characteristics

Minimum Drives: 6 (2 RAID 5 sub-arrays × 3 drives each).
Structure:
1. Create two or more RAID 5 sub-arrays (each with 3+ drives).
2. Stripe data across the RAID 5 sub-arrays (RAID 0).
Fault Tolerance: Survives 1 drive failure per sub-array (e.g., 6-drive array: 2 sub-arrays of 3 drives each – survives 1 failure in each sub-array; total 2 failures).
Capacity: (Total capacity) – (1 drive capacity per sub-array) (e.g., 6×1TB drives = 4TB usable space; 8×1TB drives = 6TB usable space).
Performance:
- Read Speed: Very high (parallel reads across all drives in all sub-arrays).
- Write Speed: High (parallel writes across sub-arrays, with parity calculated per sub-array).

Common Use Cases

High-performance enterprise storage (video streaming servers, large databases).
Data centers requiring both speed and fault tolerance.
Workloads with large sequential reads/writes (media processing, backup servers).

Pros & Cons

Pros	Cons
Excellent balance of performance, capacity, and fault tolerance	High minimum drive count (6+ drives = higher cost)
Faster rebuilds than RAID 6 (rebuild only failed sub-array)	Complex implementation and management
Higher capacity efficiency than RAID 10	Risk of total array failure if 2 drives fail in the same sub-array

Comparison of RAID Levels

Feature	RAID 0	RAID 1	RAID 2	RAID 5	RAID 6	RAID 50
Min. Drives	2	2	3	3	4	6
Fault Tolerance	None	1 (or more)	1	1	2	1 per sub-array
Usable Capacity	100%	50%	~75%	~66% (3drives)	~50% (4drives)	~66% (6drives)
Read Performance	Very High	High	High (seq)	High	High	Very High
Write Performance	Very High	Moderate	High (seq)	Moderate	Low	High
Best For	Speed (non-critical)	Critical Data	Legacy Systems	Balanced Storage	Critical Large-Scale	High-Performance Enterprise