RAID-5 vs RAID-6 vs RAID-10 — choosing for SSDs

Applying the conventional wisdom from the HDD era directly to SSDs is a loss, because rebuild time and write amplification are completely different.

rebuild risk

RAID-5 tolerates up to one disk failure. The problem is the load placed on the remaining disks during a rebuild. HDDs take tens of hours to rebuild, so the probability of a second failure during that time is not negligible.

What changes with SSDs

• Rebuild time reduced from several hours to tens of minutes
• However, write amplification increases, affecting SSD lifespan
• RAID-5/6 parity updates are especially disadvantageous for small writes

So what do we use

RAID-10 is safer for workloads with many random writes, such as VM storage. If capacity is important and the workload is mainly sequential writes, a RAID-6 + backup combination is better.

RAID is a means of availability, not a backup. If you place a backup within the same RAID, both the original and the backup are lost together in the event of a controller failure.

Practical recommendation

• VM/DB: RAID-10 + separate backup
• Large-scale archive: RAID-6 + offsite backup
• Backup targets must always be on a different physical device
• Regularly check write cache (BBU/CacheVault) status