As soon as a server hosts important data, RAID becomes essential. But between RAID 0, 1, 5, 6, and 10, which one should you choose? Each level offers a different balance between performance, usable capacity, and fault tolerance. This guide clearly compares them to help you decide — and reminds you of a key rule: RAID is not a backup.
What is RAID?
RAID (Redundant Array of Independent Disks) combines multiple disks into a single logical unit to improve performance, protect data against a disk failure, or both. It is managed by a dedicated controller (see our server components) or, less commonly, by software.
RAID Levels Explained
RAID 0 (striping)
Data is spread across multiple disks for maximum performance and capacity. No fault tolerance: if one disk fails, all data is lost. Best reserved for non-critical data (cache, temporary video editing).
RAID 1 (mirroring)
Two disks contain exactly the same data. Tolerates the failure of one disk, simple and reliable. Drawback: only half of the total capacity is available. Ideal for a small server or system.
RAID 5 (distributed parity)
Data and parity are distributed across at least 3 disks. Tolerates the failure of one disk while offering good usable capacity. The most common compromise. Note: rebuilding after a failure heavily stresses the remaining disks.
RAID 6 (double parity)
Like RAID 5, but tolerates the failure of two disks simultaneously (minimum 4 disks). Safer for large arrays and high-capacity disks, at the cost of slightly reduced usable capacity.
RAID 10 (mirroring + striping)
Combines the security of mirroring with the performance of striping (minimum 4 disks). Excellent read/write performance and good fault tolerance. Often the choice for databases and virtualization — but half the capacity is dedicated to mirroring.
There are also combinations like RAID 50 or 60 for very large arrays.
Tip: estimate your array’s usable capacity and fault tolerance based on the level, number, and size of disks with our RAID calculator.
Hardware RAID or Software RAID?
Hardware RAID (dedicated controller, like Dell’s PERC) offloads the CPU, manages cache and hot-swap: it’s the server standard. Software RAID (managed by the system) is cheaper but uses CPU resources. For a production server, hardware controllers are still recommended.
How to Choose Based on Usage
- Small server/system → RAID 1.
- File server, good capacity/security balance → RAID 5.
- Large array, high-capacity disks → RAID 6.
- Databases, virtualization, performance → RAID 10.
If possible, plan for a hot spare disk to automatically start rebuilding in case of failure. To choose your disks (SAS, SATA, SSD), see our guide HDD, SSD, SAS, SATA and our hard drives & SSDs.
RAID Is Not a Backup
Golden rule: RAID protects against hardware disk failure, not accidental deletion, ransomware, or disasters. A true backup (external copy or on LTO tape) remains essential, following the 3-2-1 rule.
FAQ: RAID Levels
Which RAID is the safest?
RAID 6 (tolerates two failures) and RAID 10 (high-performance mirroring) are the safest. The choice depends on the trade-off between capacity and performance.
RAID 5 or RAID 10?
RAID 5 maximizes usable capacity; RAID 10 favors performance and write robustness. For databases, RAID 10 is often preferred.
How many disks are needed?
RAID 1: 2 disks. RAID 5: minimum 3. RAID 6 and RAID 10: minimum 4. The larger the array, the more relevant RAID 6 becomes.
Does RAID replace a backup?
No. It ensures continuity in case of a disk failure but does not protect against deletions, viruses, or disasters. Always back up in addition.
In Summary
Choosing a RAID level means balancing performance, usable capacity, and fault tolerance: RAID 1 for simplicity, RAID 5 for compromise, RAID 6 for large array security, RAID 10 for performance. Prefer a hardware controller, add a hot spare — and never forget backups. With tested used hardware, controllers and disks are much more affordable.