RAID 5 vs RAID 6
What Is the Main Difference Between RAID 5 and RAID 6?
The fundamental difference is parity protection. RAID 5 uses one distributed parity block per stripe and can tolerate one failed drive. RAID 6 uses two independent distributed parity blocks per stripe and can tolerate two failed drives.
RAID 5 therefore provides more usable capacity for the same number and size of drives. RAID 6 sacrifices the equivalent capacity of one additional drive and performs additional parity work in exchange for substantially greater drive-failure tolerance.
RAID 5 vs RAID 6 at a Glance
| Characteristic | RAID 5 | RAID 6 |
|---|---|---|
| Architecture | Striping + distributed parity | Striping + dual distributed parity |
| Minimum Drives | 3 | 4 |
| Parity Overhead | 1 drive equivalent | 2 drives equivalent |
| Drive-Failure Tolerance | 1 drive | 2 drives |
| Usable Capacity Formula | (N − 1) × smallest drive | (N − 2) × smallest drive |
| Capacity Efficiency | Higher for the same drive count | Lower due to second parity equivalent |
| Read Performance | Generally strong | Generally strong |
| Small-Write Overhead | Lower parity overhead | Higher due to dual parity |
| Protection After One Drive Fails | No additional drive-failure tolerance | Can tolerate one additional drive failure |
Single Distributed Parity
RAID 5 stripes data across all members while distributing parity information across the array. The parity provides enough redundant information to reconstruct the contents of one failed member drive.
Dual Distributed Parity
RAID 6 extends the parity concept by maintaining two independent parity values across each stripe. This additional redundancy allows the array to reconstruct data following the simultaneous loss of as many as two member drives.
How Much Capacity Do RAID 5 and RAID 6 Provide?
These formulas assume drives of equal usable size. When drives differ in capacity, traditional RAID implementations generally limit each member's contribution to the usable capacity of the smallest drive.
RAID 5 vs RAID 6 With Eight 8 TB Drives
(8 − 1) × 8 TB = 56 TB
(8 − 2) × 8 TB = 48 TB
One Drive Can Fail
RAID 5 remains operational following one member-drive failure. During this degraded state, the missing information must be reconstructed from the remaining data and parity.
Until redundancy is restored, another required member-drive failure exceeds RAID 5's single-parity protection and can result in loss of the RAID set.
Two Drives Can Fail
RAID 6 can remain operational following the simultaneous loss of up to two member drives because two independent parity values are maintained.
Following the first failure, RAID 6 therefore retains protection against one additional member-drive failure while the array is degraded.
The Rebuild Window Is an Important RAID 5 vs RAID 6 Difference
After one RAID 5 member fails, the array has exhausted its drive-failure tolerance until redundancy is restored. RAID 6, by contrast, still has one remaining level of drive-failure protection after its first member failure.
This distinction becomes especially relevant when rebuilds take substantial time. Rebuild duration is not a fixed RAID-level number: it varies with drive capacity and speed, controller behavior, rebuild priority, array width, workload, interface bandwidth, and other implementation factors.
Is RAID 5 Faster Than RAID 6?
Both RAID 5 and RAID 6 can provide strong read performance because data is striped across multiple drives. Actual throughput depends on array width, drives, controller, cache, workload and interface limits.
Both levels incur parity-related write overhead. RAID 6 must maintain two parity values instead of one, so its parity processing and update requirements are greater.
RAID level alone cannot predict exact MB/s or IOPS. Controller architecture, write-back cache, SSD or HDD media, queue depth, stripe size and workload pattern can materially change performance.
Why RAID 6 Has More Small-Write Overhead
A small partial-stripe parity write can require existing data and parity information to be read, updated parity to be calculated, and both data and parity to be written back. RAID 6 maintains two parity values, increasing the amount of parity work compared with RAID 5.
Traditional RAID write-penalty formulas are useful for modeling I/O operations, but they should not be interpreted as fixed real-world performance percentages. Modern RAID controllers, cache, full-stripe writes and workload characteristics can significantly change observed performance.
Greater Usable Capacity
With the same number and capacity of drives, RAID 5 provides one additional drive-equivalent of usable storage compared with RAID 6. This can lower the number of drives required to reach a particular usable-capacity target.
Greater Failure Protection
RAID 6 exchanges that additional drive-equivalent of usable capacity for dual parity. The array remains protected against another member-drive failure after the first failure occurs.
RAID 5 or RAID 6: Which Should You Choose?
There is no universally correct choice. The better RAID level depends on usable-capacity requirements, acceptable failure risk, drive count, drive capacity, rebuild characteristics, workload, controller capabilities, performance requirements and the importance of the data being stored.
- Capacity efficiency is a major priority.
- The array is relatively small.
- Single-drive fault tolerance meets the design requirement.
- Additional parity overhead is undesirable.
- Independent backups and recovery procedures are already in place.
- Dual-drive fault tolerance is important.
- The array uses larger-capacity drives.
- Rebuilds may require significant time.
- Maintaining protection after the first failure is important.
- The additional parity-capacity cost is acceptable.
A Hot Spare Does Not Turn RAID 5 Into RAID 6
A hot spare is an available replacement drive that supported RAID implementations can use to begin rebuilding after a member fails. It does not provide RAID 6's second independent parity value. Until a RAID 5 rebuild completes and redundancy is restored, the degraded RAID 5 set remains unable to tolerate another required member-drive failure.
Calculate RAID 5 vs RAID 6 for Your Drives
Use the Tech Supply Direct RAID Calculator to compare usable capacity, storage efficiency, parity overhead, fault tolerance, estimated performance, hot-spare impact and hardware cost across RAID configurations.
RAID 5 vs RAID 6 FAQ
Is RAID 6 safer than RAID 5?
RAID 6 provides greater drive-failure tolerance because it can tolerate two failed member drives, while RAID 5 can tolerate one.
Does RAID 6 have less usable capacity?
Yes. RAID 5 consumes the equivalent capacity of one drive for parity, while RAID 6 consumes the equivalent capacity of two drives.
Is RAID 5 faster than RAID 6?
RAID 5 generally requires less parity work for writes. RAID 6 maintains two parity values, adding write overhead. Exact performance depends heavily on the implementation, hardware and workload.
What happens after one drive fails?
RAID 5 has exhausted its drive-failure tolerance until redundancy is restored. RAID 6 can still tolerate one additional member-drive failure.
Does a hot spare make RAID 5 equivalent to RAID 6?
No. A hot spare can provide a replacement target for a rebuild, but it does not add a second independent parity value to RAID 5.
Does RAID 5 or RAID 6 replace backups?
Neither does. RAID protects against supported drive-failure scenarios; it does not replace independent backups for important data.
Related RAID Resources
RAID Is Not a Backup
RAID 5 and RAID 6 provide redundancy against supported drive-failure scenarios, but neither protects against every cause of data loss. Accidental deletion, corruption, ransomware, application errors, catastrophic hardware loss and other events can still affect data. Important information should also be protected with independent, tested backups.