When setting up a RAID array for a server or storage system, two of the most common options are RAID 10 and RAID 6. Both provide fault tolerance through striping and mirroring/parity, but they have key differences in performance, capacity overhead, and rebuild times. This article will examine the pros and cons of each in depth to help you decide which is better for your needs.
What is RAID?
RAID stands for Redundant Array of Independent Disks. It is a data storage technology that combines multiple disk drives into a logical unit. RAID takes advantage of the parallelism of multiple disks to enhance capacity, performance, or reliability compared to a single disk.
There are several standard RAID levels, each with specific data distribution and fault tolerance characteristics:
|Data striping across disks for performance, no redundancy
|Disk mirroring for redundancy, no performance gain
|Block-level striping with distributed parity, single disk fault tolerance
|Block-level striping with double distributed parity, two disk fault tolerance
|Stripe of mirrors, mirroring plus striping for redundancy and performance
Higher RAID levels provide greater fault tolerance, while lower levels aim for better performance. When choosing a RAID level, it’s important to balance your needs for speed, capacity, and reliability.
What is RAID 10?
RAID 10, also known as RAID 1+0, is a nested RAID array that combines mirroring and striping. It requires a minimum of four disks.
In RAID 10, the disks are paired up and mirrored. Each disk pair forms a RAID 1 array. The RAID 1 arrays are then striped together in a RAID 0 configuration. This provides both the performance benefits of RAID 0 striping and the fault tolerance of RAID 1 mirroring.
Advantages of RAID 10:
- High read/write performance – spreading I/O across many disks improves throughput
- Capacity overhead is only 50% – RAID 10 array size is half of total disk space
- Highly fault tolerant – can survive multiple disk failures if in separate mirror pairs
- Rebuild times are fast after drive failure – only one mirror needs rebuilding
Disadvantages of RAID 10:
- Relatively expensive – requires a minimum of 4 disks
- Usable capacity is half of installed disks – RAID 10 only stores one copy of data
RAID 10 works best for applications that demand faster data access, have high I/O workloads, and require continuous uptime. The performance gains make it well-suited for transactional databases, web/app servers, virtualization, and critical systems where downtime must be minimized.
What is RAID 6?
RAID 6 extends the distributed parity approach of RAID 5 to add a second parity block. It requires a minimum of 4 disks.
In RAID 5, data and parity blocks are striped across the disks. The parity block can be used to reconstruct data if a disk fails. But if a second disk fails before rebuilding occurs, data will be lost.
RAID 6 overcomes this limitation by calculating and writing a second, independent parity block across the disks. This provides protection against the failure of up to two disks.
Advantages of RAID 6:
- High fault tolerance – survives up to two disk failures
- Capacity overhead is low – only requires 2 disks for parity
- Rebuilding RAID 6 after drive failure is simpler than RAID 10
- RAID 6 arrays can be expanded by adding disks
Disadvantages of RAID 6:
- Slower read/write speeds – parity calculation and write penalty reduce throughput
- Long rebuild times – rebuilding two parity disks is time consuming
- Writing the two parity blocks increases disk write workload
The dual parity of RAID 6 makes it ideal for large storage arrays, NAS devices, and enterprise servers that need both high capacity and reliability. The lower cost compared to RAID 10 also makes it more feasible for bulk data storage scenarios.
Comparing RAID 10 and RAID 6
Now that we’ve looked at RAID 10 and RAID 6 individually, let’s compare them across a few key factors:
RAID 10 provides faster read and write speeds than RAID 6. The mirrored disks allow for high levels of parallelism for I/O requests. Writes don’t incur a parity calculation penalty.
RAID 6 write speeds suffer due to the need to calculate and update both parity blocks. This write penalty can significantly impact write-heavy workloads. Rebuilding a RAID 6 array after a disk failure also takes longer than with RAID 10.
Winner: RAID 10
RAID 10’s need to mirror disks results in a 50% capacity overhead. Only half of installed disks store unique user data.
RAID 6 has relatively low overhead – just two disks are needed for redundant parity space. This efficiency makes it easy to scale to large capacities by adding more data disks.
Winner: RAID 6
Both RAID 10 and RAID 6 can withstand a single disk failure without data loss. However, RAID 6 offers protection against a second disk failure that RAID 10 lacks. This makes it more resilient for large arrays.
That said, rebuilding a failed RAID 10 disk is simpler and faster than rebuilding two failed disks in RAID 6.
Overall for fault tolerance: Tie
RAID 10 has higher hardware costs, since it requires a minimum of 4 disks plus 50% capacity overhead. More disks are needed for usable space.
RAID 6 has lower initial cost due to its efficient use of installed disks. Adding capacity is also cheaper with RAID 6 – just add more large SATA drives.
Winner: RAID 6
When to choose RAID 10 over RAID 6
Based on the comparison, RAID 10 excels for applications needing high performance, while RAID 6 is preferable when large capacity and high reliability are critical.
RAID 10 is the better choice in these scenarios:
- Transactional database servers that require low latency
- High volume web servers and load balancers
- High performance virtualization hosts
- Systems that demand faster rebuilds after a disk failure
- Critical applications where uptime is crucial
The speed of RAID 10 outweighs the capacity and cost limitations for these use cases. Performance and uptime take priority over storage density.
When to choose RAID 6 instead
Pick RAID 6 if these factors are most important:
- You need very large amounts of storage space
- You want good read performance but write speed is less important
- You are on a tight hardware budget
- Rebuild time after a failure is not critical
RAID 6 offers slower but fully reliable performance plus massive scalable capacity. The dual redundancy also brings peace of mind for critical data storage needs:
- Archive repositories and data lakes
- Media libraries and video surveillance storage
- Backup systems and disaster recovery
For these use cases, the higher capacity and incremental scaling of RAID 6 outweighs the performance limits compared to RAID 10.
RAID 10 and RAID 6 both have benefits depending on your priorities. RAID 10 is great for I/O performance and uptime, while RAID 6 efficiently provides vast capacity with double redundancy.
If your applications are highly sensitive to latency and downtime, choose RAID 10. But if you need tons of reliable storage space on a budget, go with RAID 6. Understanding the strengths of each will help you pick the right RAID level for your needs.
With the ever-growing demand for storage, utilize both RAID 10 and RAID 6 where appropriate to maximize the performance, capacity, and resilience of your environment.