When setting up a RAID configuration for a storage system, two popular options are RAID 6 and RAID 10. Both provide fault tolerance through redundancy, but they achieve it in different ways. RAID 6 offers strong protection against drive failures and is efficient with storage capacity, while RAID 10 optimizes performance and throughput. There are pros and cons to each that should factor into the decision between the two.
Quick Answers
Here are quick answers to common questions about choosing between RAID 6 and RAID 10:
- RAID 6 can tolerate up to two drive failures without losing data, while RAID 10 can only handle one drive failure.
- RAID 6 offers better overall storage capacity efficiency than RAID 10.
- RAID 10 provides faster read/write speeds and better performance for demanding applications.
- RAID 6 rebuild times are slower than RAID 10.
- RAID 10 requires a minimum of 4 drives, while RAID 6 needs at least 3 drives.
- RAID 10 handles small random reads/writes better than RAID 6.
- RAID 6 is generally more cost effective as drives sizes increase over time.
In general, RAID 6 is preferred for data protection and storage efficiency, while RAID 10 is better for peak performance. The needs of the specific storage environment should drive the decision between the two.
What is RAID 6?
RAID 6, also known as double parity RAID, uses block-level striping with two parity stripes distributed across all member disks. This configuration can tolerate failure of up to two drives without losing access to data. If a drive fails, the array remains functional, and data can still be accessed and read. Then the failed drive can be replaced and rebuilt via the parity data.
A minimum of three drives is required for RAID 6. The two parity strips provide redundancy. Since parity information needs to be stored, the total storage capacity of a RAID 6 array is the capacity of member disks minus two disks worth of capacity. For example, an array of five 2 TB drives would have 6 TB of usable space in RAID 6. The 2 TB lost to parity is considered the cost of the fault tolerance provided.
Because RAID 6 can withstand two disk failures, it offers excellent protection against potential data loss. The dual parity provides peace of mind against multiple drive failures causing data unavailability. RAID 6 is considered one of the most reliable and robust RAID configurations.
Advantages of RAID 6
- Can tolerate up to 2 drive failures without data loss
- Provides excellent fault tolerance and redundancy
- More efficient use of storage capacity versus RAID 10
- Supported in most major RAID implementations
- Cost effective as drive sizes increase over time
Disadvantages of RAID 6
- Slower write performance than RAID 10
- Slow rebuild times compared to RAID 10
- Higher computational overhead for dual parity calculation
- At least 3 drives required
What is RAID 10?
RAID 10, also known as RAID 1+0, combines both mirroring and striping for redundancy and performance. It requires a minimum of four drives configured as two mirrored pairs whose data is then striped across the pairs. This provides fault tolerance along with fast I/O operations.
In RAID 10, if a single drive fails, the mirror for that pair will continue functioning from the remaining drive. This allows data to still be accessed with no downtime. The failed drive can then be replaced and added back to the array to restore redundancy.
Because RAID 10 duplicates all data across mirrored drives, it requires a minimum of four disks for a two drive mirror. The total storage capacity of the array is equal to the capacity of the member disks divided by two for the mirrors. For example, four 2 TB drives would provide 2 TB of usable space in RAID 10.
Advantages of RAID 10
- Excellent performance for reads and writes
- Very fast rebuild times
- Can tolerate a single drive failure without downtime
- Ideal for transactional workloads needing high IOPS
- Handles small random reads/writes very efficiently
Disadvantages of RAID 10
- Only can handle a single drive failure
- High storage capacity overhead due to mirroring
- Requires a minimum of four drives
- More expensive than RAID 6 as drive sizes increase
Comparing Fault Tolerance
One of the main differences between RAID 6 and RAID 10 is in their fault tolerance capabilities:
- RAID 6 can withstand failure of up to 2 drives without data loss.
- RAID 10 can only handle a single drive failure without loss of data.
This makes RAID 6 the better option for maximum redundancy. The dual parity stripes provide an extra layer of protection compared to RAID 10. If your priority is protecting against multiple drive failures causing data unavailability, then RAID 6 would be the preferred solution.
Rebuild Times
In addition to withstanding more drive failures, rebuilding degraded arrays is also faster with RAID 10 than RAID 6. Because RAID 10 simply needs to copy mirror data to a replacement drive, rebuilds complete very quickly. RAID 6 requires more computation to rebuild the dual parity data, so rebuilds take much longer.
If your storage environment demands maximum uptime and availability, the faster rebuild capability of RAID 10 can be a notable advantage. But for many use cases, the slower RAID 6 rebuild process is acceptable to gain its extra fault tolerance.
Comparing Performance
For applications needing high performance, RAID 10 will generally provide better results than RAID 6. The mirrored striping maximizes speed for both reads and writes across multiple drives.
Reads
RAID 10 reads perform very well, as data can be read in parallel from multiple drives at the same time. Large striped reads across drives provides significant performance gains.
RAID 6 read operations also see gains from striping, though some overhead occurs from needing to calculate parity data. But overall, the performance difference for reads between RAID 10 and RAID 6 is smaller compared to writes.
Writes
Writes see the biggest performance difference between the two RAID levels. RAID 10 can stripe writes across all drives for excellent performance. Writes to both copies of mirrored data happen in parallel.
For RAID 6, write operations bear the brunt of the dual parity calculation overhead. The parity data needs to be read and recalculated for every write, which adds substantial latency. RAID 10’s write performance advantage over RAID 6 is often 2-3x for typical use cases.
Caching
The addition of read/write caching can help improve RAID 6 write speeds closer to RAID 10. But ultimately, RAID 10 still provides lower latency and higher input/output operations per second (IOPS) for demanding workloads. Databases and other transactional applications where writes dominate will see significant gains with RAID 10.
Comparing Storage Efficiency
Due to its mirroring, RAID 10’s storage efficiency is low compared to RAID 6. Depending on the number of disks, RAID 10’s capacity overhead can be anywhere from 50% to 66%.
RAID 6 has much better overall efficiency, with a fixed overhead of just two disks worth of capacity. This overhead percentage also decreases significantly as member disk capacity increases.
Example Storage Efficiency
| RAID Level | Drives | Drive Size | Total Capacity | Usable Capacity | Efficiency % |
|---|---|---|---|---|---|
| RAID 10 | 4 x 2 TB | 2 TB | 8 TB | 4 TB | 50% |
| RAID 6 | 5 x 2 TB | 2 TB | 10 TB | 8 TB | 80% |
This example highlights the capacity efficiency advantage of RAID 6. For the same number of raw drives, RAID 6 provides double the usable space as RAID 10 configuration. As drive capacities continue to increase, this efficiency difference becomes even more pronounced.
Minimum Number of Drives
Due to its dual parity requirement, the minimum number of drives needed for RAID 6 is 3. RAID 10 requires a minimum of 4 drives, with at least 2 mirrors, to provide data redundancy.
If you only have a smaller number of drives available, RAID 10 may not be an option. The drive requirements should be considered when choosing between the RAID levels.
Choosing RAID 6 vs RAID 10
So when should you choose RAID 6 over RAID 10, and vice versa? Here are some general guidelines and considerations for each scenario:
Choose RAID 6 If:
- Data protection and redundancy are critical – RAID 6 offers the best fault tolerance against drive failures
- Storage capacity efficiency is important – RAID 6 provides significant efficiency advantages
- Cost is a factor – As drive sizes increase, RAID 6 becomes much more cost effective than RAID 10
- Rebuild time is not critical – Slower rebuilds may be acceptable
- Write performance needs are moderate – Many workloads run fine on RAID 6
- You have at least 3 drives available
Choose RAID 10 If:
- Maximum read/write performance is needed – RAID 10 excels at IOPS
- Low latency and response times are critical
- Availability and uptime are paramount – Fast rebuilds minimize downtime
- Small random writes will dominate – RAID 10 handles these very efficiently
- Budget allows for extra cost of RAID 10
- You have at least 4 drives available
Conclusion
RAID 6 and RAID 10 offer complementary strengths and weaknesses. RAID 6 emphasizes data protection and capacity, while RAID 10 optimizes for speed and uptime. Consider the specific needs of your environment and applications when deciding which solution makes the most sense. Analyze your workload’s read/write characteristics, performance requirements, number of available drives, fault tolerance needs and budget.
For most general-purpose applications that don’t require extreme performance, RAID 6 provides an excellent blend of storage efficiency, redundancy, and reasonable speeds. But transactional databases and I/O intensive applications will benefit from the faster mirrored writes of RAID 10. As drive capacities continue increasing, RAID 6 also becomes much more cost effective than RAID 10.
By understanding the core differences between RAID 6 and RAID 10, you can select the right approach to meet your specific storage needs and deliver a robust, high performance RAID implementation.