Alternative RAID Levels: RAID 5, RAID 6, and When to Consider Them

RAID 5 and RAID 6 are popular alternative RAID levels that balance performance, capacity, and fault tolerance, but they differ mainly in data protection and rebuild characteristics.

• RAID 5 stripes data and parity across all drives, allowing the array to survive a single drive failure without data loss. It offers better write performance and faster rebuild times compared to RAID 6, typically maintaining about 80% of normal performance during rebuilds. RAID 5 also provides higher usable capacity (about 85-90% of raw capacity) since it uses single parity. However, it is more vulnerable to data loss if a second drive fails during rebuild or power failure scenarios.

• RAID 6 extends RAID 5 by adding a second parity block, allowing it to tolerate two simultaneous drive failures. This makes RAID 6 more fault tolerant and safer for critical data, especially in larger arrays or environments where rebuild times are long. The tradeoff is a write performance penalty due to double parity calculations, slower rebuilds (about 1.5 times longer), and slightly reduced usable capacity (around 75-85%). RAID 6 typically operates at 60-70% capacity during rebuilds and offers better data preservation in power failures (up to 90% better than RAID 5).

When to consider RAID 5:

• You need a good balance of performance, capacity, and fault tolerance.
• Your environment can tolerate the risk of a single drive failure.
• Faster rebuild times are important.
• Cost sensitivity is a factor, as RAID 5 has lower overhead than RAID 6.

When to consider RAID 6:

• Data protection is a higher priority, especially for critical or large datasets.
• You want to guard against two simultaneous drive failures.
• You can accept slightly lower write performance and longer rebuild times.
• Your system may experience power failures or other risks during rebuilds.
• You are willing to invest more in hardware and maintenance for better fault tolerance.

Both RAID 5 and RAID 6 work well with SSDs, with RAID 5 showing better write performance due to less parity overhead, while RAID 6 offers superior data protection. The choice depends on your specific needs for performance, capacity, and fault tolerance.