RAID Levels Explained

RAID 0 - Striping

How It Works

RAID 0 splits data across multiple drives (striping) without any redundancy. Each file is divided into blocks that are written to different drives simultaneously, maximizing performance and capacity.

Capacity Formula

Example: 4× 4TB drives = 16TB usable

Pros

• Maximum storage efficiency (100% capacity)
• Excellent read and write performance
• Simple to implement
• Low cost per TB

Cons

• No redundancy - any drive failure loses all data
• Higher failure risk with more drives (N-times the AFR)
• Not suitable for critical data

Best Use Cases

• Video editing scratch disks
• Gaming storage with backups elsewhere
• Temporary data processing
• Cache or staging areas
• When performance matters more than data safety

RAID 1 - Mirroring

How It Works

RAID 1 creates an exact copy (mirror) of data on two or more drives. Every write operation is duplicated to all drives in the mirror set, providing complete redundancy.

Capacity Formula

Example: 4× 4TB drives = 8TB usable (50% efficiency)

Pros

• Simple and reliable redundancy
• Fast read performance (can read from multiple drives)
• Quick rebuild time (just copy the mirror)
• Can survive one drive failure
• No complex parity calculations

Cons

• 50% capacity efficiency (expensive per TB)
• Write performance same as single drive
• Not ideal for large arrays (RAID 5/6 better for 4+ drives)

Best Use Cases

• 2-bay NAS systems
• Boot/OS drives requiring redundancy
• Database transaction logs
• Critical data with 2-4 drives
• When simplicity and reliability are priorities

RAID 1E - Enhanced Mirroring

How It Works

RAID 1E is an enhancement of RAID 1 that supports odd numbers of drives by distributing mirrored data across all drives in a striped pattern. Unlike RAID 1, which creates discrete mirror pairs, RAID 1E distributes mirrors across the array.

Key Differences from RAID 1

• Supports odd number of drives (3, 5, 7, etc.)
• Better rebuild performance (uses all drives)
• More flexible than traditional RAID 1
• Mirrors are offset/staggered across drives

Best Use Cases

• When you have an odd number of drives
• Better rebuild performance than RAID 1 needed
• 3 or 5-bay systems where RAID 5 isn't desired

RAID 10 - Mirrored Stripes (RAID 1+0)

How It Works

RAID 10 combines mirroring (RAID 1) and striping (RAID 0). Drives are paired into mirrors first, then data is striped across the mirror pairs. This provides both high performance and redundancy.

Capacity Formula

Example: 8× 4TB drives = 16TB usable (4 mirror pairs, 50% efficiency)

Pros

• Excellent read and write performance
• High redundancy (can survive multiple failures if they're in different pairs)
• Fast rebuild (just copy the mirror)
• No parity calculation overhead
• Better random I/O than RAID 5/6

Cons

• 50% capacity efficiency (expensive)
• Requires even number of drives (minimum 4)
• Can fail if both drives in a mirror pair fail

Best Use Cases

• Database servers (SQL, Oracle, MongoDB)
• High-transaction applications
• Virtual machine datastores
• Email servers
• When both performance and redundancy are critical
• 4-8 drive systems with high I/O workloads

RAID 5 - Single Parity Striping

How It Works

RAID 5 stripes data and parity information across all drives. Parity allows the array to reconstruct data if one drive fails. The parity is distributed evenly so no single drive is a bottleneck.

Capacity Formula

Example: 5× 4TB drives = 16TB usable (80% efficiency)

Pros

• Good balance of capacity, performance, and redundancy
• Better capacity efficiency than RAID 1/10
• Good read performance
• Industry standard for 3-8 drive arrays

Cons

• Write performance penalty due to parity calculations
• Vulnerable during rebuild (no redundancy if another drive fails)
• URE risk with large drives (>8TB) - consider RAID 6
• Slow rebuild times on large drives
• Poor random write performance

Best Use Cases

• General-purpose file servers
• NAS with 3-6 drives of ≤8TB each
• Media storage (read-heavy workloads)
• Backup targets
• When capacity efficiency matters more than write speed

RAID 6 - Dual Parity Striping

How It Works

RAID 6 extends RAID 5 by using two independent parity calculations. This allows the array to survive two simultaneous drive failures. The dual parity provides significantly better protection during rebuilds and for large-capacity drives.

Capacity Formula

Example: 8× 12TB drives = 72TB usable (75% efficiency)

Pros

• Can survive two simultaneous drive failures
• Much safer during rebuild than RAID 5
• Recommended for drives >8TB
• Better URE protection during rebuild
• Good for mission-critical data

Cons

• Lower capacity efficiency than RAID 5 (two parity drives)
• Worse write performance than RAID 5 (more parity overhead)
• Longer rebuild times
• Requires minimum 4 drives (not efficient until 6+)

Best Use Cases

• Arrays with large drives (8TB-24TB)
• Mission-critical data requiring high availability
• Archival storage (write-once, read-many)
• When two-drive failure protection is needed
• 6-24 drive enterprise arrays
• 24/7 production environments

RAID 5E & 5EE - Enhanced RAID 5

How They Work

RAID 5E and 5EE are variants of RAID 5 with integrated distributed spare capacity. Instead of dedicating entire drives as hot spares, the spare capacity is distributed across all drives.

RAID 5E: Integrates spare space equivalent to one drive distributed across the array.
RAID 5EE: Enhanced version with better spare distribution and potentially better performance.

Capacity Formula

Advantages Over RAID 5

• Faster rebuild (uses spare capacity distributed across all drives)
• Better performance during rebuild
• Automatic spare integration (no dedicated hot spare needed)

Best Use Cases

• When faster rebuild than RAID 5 is desired
• Systems where hot spare management is complex
• Controllers that support these levels natively

RAID 50 - Striped RAID 5 (RAID 5+0)

How It Works

RAID 50 combines RAID 5 and RAID 0. Multiple RAID 5 arrays (minimum 2 groups) are striped together. This provides better performance than single RAID 5 while maintaining single-drive fault tolerance per RAID 5 group.

Capacity Formula

Example: 12 drives in 2 groups of 6 = 2 × 5 × 4TB = 40TB usable (83% efficiency)

Pros

• Better write performance than single RAID 5
• Improved fault tolerance across groups
• Faster rebuild than large single RAID 5
• Suitable for large drive counts (12-24 drives)

Cons

• Complex setup and management
• Requires minimum 6 drives (not cost-effective below 8-12)
• Can fail if two drives in same RAID 5 group fail
• Lower capacity efficiency than RAID 5 (multiple parity drives)

Best Use Cases

• Large storage arrays (12-24 drives)
• High-performance file servers
• Video surveillance systems
• When RAID 5 performance isn't enough but RAID 10 too expensive

RAID 60 - Striped RAID 6 (RAID 6+0)

How It Works

RAID 60 is RAID 6 + RAID 0. Multiple RAID 6 arrays are striped together. This provides the ultimate combination of performance, capacity, and redundancy for very large enterprise arrays.

Capacity Formula

Example: 16 drives in 2 groups of 8 = 2 × 6 × 12TB = 144TB usable (75% efficiency)

Pros

• Maximum redundancy (two drive failures per group)
• Excellent for very large drives and massive arrays
• Better performance than single RAID 6
• Can survive multiple drive failures across groups
• Safer rebuild than RAID 50

Cons

• Very complex to set up and manage
• Expensive (requires minimum 8 drives)
• Lower capacity efficiency than RAID 50
• Write performance penalty from dual parity

Best Use Cases

• Enterprise data centers
• Mission-critical storage with 16-48 drives
• Large-capacity archive systems
• When maximum data protection is required
• Cloud storage providers
• Big data applications requiring both performance and reliability