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Usage estimate

RAID types
Not enough drives — need at least 3
Not enough drives — need at least 4

Results are based on a binary storage calculation, not decimal.

Reserved capacity for system1
Available capacity2
Protection
Unused space

1 A small portion of storage is reserved for system use and internal management.

2 Actual available capacity may vary depending on file system and usage conditions.

What Is RAID? Understanding RAID Levels for NAS and Storage

RAID (Redundant Array of Independent Disks) is a technology that combines multiple physical drives into a single logical unit to improve performance, add data redundancy, or both. It's widely used in NAS devices, servers, and workstations where protecting against disk failure or maximizing throughput matters. The RAID calculator above shows usable storage and fault tolerance for each RAID level so you can compare configurations before you buy.

RAID 0 — Striping for Performance

RAID 0 stripes data across all drives, giving you the full combined capacity and the fastest read/write speeds of any RAID level. The trade-off is zero redundancy — if any single drive fails, all data is lost. RAID 0 is best suited for scratch disks, caches, or temporary storage where speed matters more than durability.

RAID 1 — Mirroring for Redundancy

RAID 1 mirrors data identically across two drives. You get the capacity of a single drive (half the raw total), but the array survives a complete disk failure with no data loss. Read speeds can be faster because either drive can serve a request, while write speeds are limited by the slowest disk. RAID 1 is a common choice for OS drives and critical small datasets on a NAS.

RAID 5 — Distributed Parity

RAID 5 distributes parity information across all drives in the array, allowing the loss of any one disk without data loss. Usable storage equals the total raw capacity minus one drive's worth. A minimum of three drives is required. RAID 5 balances storage efficiency, performance, and data redundancy, making it one of the most popular RAID levels for NAS storage.

RAID 6 — Double Parity for Larger Arrays

RAID 6 extends RAID 5 with a second parity block, allowing any two drives to fail simultaneously without losing data. This comes at the cost of two drives' worth of capacity overhead and slightly lower write performance. RAID 6 is recommended for arrays with four or more large drives where rebuild times are long enough that a second failure during rebuild is a real risk.

RAID 10 — Speed and Redundancy Combined

RAID 10 (also written RAID 1+0) combines mirroring and striping: drives are first paired into mirrored sets, then those sets are striped together. You get the read/write performance of striping with the fault tolerance of mirroring. Usable storage is half the total raw capacity, and a minimum of four drives is required. RAID 10 is ideal for high-performance databases and workloads that need both speed and reliability.

RAID Is Not a Backup

RAID protects against hardware failure, but it does not protect against accidental deletion, ransomware, file corruption, or a catastrophic event that destroys the whole array. Every RAID configuration still needs a separate backup strategy — ideally following the 3-2-1 rule: three copies of data, on two different media types, with one copy offsite. RAID and backups solve different problems and are both necessary for serious data protection.

Ready to go deeper? Our RAID guides cover drive selection, NAS setup, and storage planning in more detail.