RAID is a way of combining multiple hard drives or SSDs to improve storage capacity, performance, or fault tolerance. It is commonly used in NAS systems, servers, and even some custom-built PCs.
If you are wondering what RAID means, how RAID 0, RAID 1, RAID 5, RAID 6, and RAID 10 differ, or which RAID level is best for your setup, this guide explains the basics in a simple way.
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RAID changes the balance between three things: capacity, speed, and data protection.
RAID stands for Redundant Array of Independent Disks. It is a technology that lets multiple drives work together as one storage system.
Depending on the RAID level, you can use RAID to increase usable storage, improve read and write performance, or keep your data available even if one or more drives fail.
In other words, RAID is not just about using more disks. It is about choosing how your storage system should behave.
Most RAID levels are built from three basic ideas:
Each RAID level uses these ideas in a different way.
RAID 0 stripes data across multiple disks. It can improve performance and uses the full capacity of all drives, but it provides no redundancy. If one disk fails, all data in the array is lost.
RAID 1 mirrors the same data across disks. It is simple and safe, which makes it a popular choice for 2-bay NAS devices. The downside is that usable capacity is limited to one disk.
RAID 5 stripes data and stores parity across the array. It offers a good balance of usable capacity and fault tolerance, which is why it is popular for home NAS systems with four or more drives.
RAID 6 is similar to RAID 5, but it uses double parity. That means it can survive two disk failures instead of one. The tradeoff is lower usable capacity and somewhat slower writes.
RAID 10 combines mirroring and striping. It offers strong performance and good redundancy, but it requires more disks and only half of the total raw capacity is usable.
| RAID Level | Capacity Efficiency | Performance | Fault Tolerance | Main Strength |
|---|---|---|---|---|
| RAID 0 | High | Fast | None | Capacity and speed |
| RAID 1 | Low | Moderate | High | Simple and safe |
| RAID 5 | High | Good overall | One disk failure | Balanced option |
| RAID 6 | Medium | Writes can be slower | Two disk failures | Higher protection |
| RAID 10 | Medium | Fast | High | Speed and redundancy |
There is no single best RAID level for everyone. The right choice depends on what matters most in your storage setup.
For home NAS use, RAID 1 and RAID 5 are often the most practical options.
If you are using large hard drives and care about rebuild safety, RAID 6 can be more attractive than RAID 5.
This is one of the most important things to understand. RAID can protect against disk failure, but it does not protect against accidental deletion, malware, ransomware, fire, theft, or other disasters.
If you delete a file from a RAID array, the file is still deleted. That is why you should always keep a separate backup of important data.
Usable capacity changes depending on the RAID level, the number of disks, and the size of each disk. If you want to understand the formulas in more detail, read:
RAID Capacity Calculation Guide
If you want to calculate it instantly, use:
RAID 5 and RAID 6 are often compared for NAS and server use. If you want a more detailed look at the difference between capacity efficiency and safety, read this comparison: