RAID (Redundant Array of Independent Disks) is a data storage technology that combines multiple disk drive components into a logical unit. RAID provides fault tolerance by allowing data to be distributed across multiple disks. If one disk fails, the data can still be accessed from the remaining disks. There are several different RAID levels, each with its own mix of performance, capacity and fault tolerance.
Two commonly used RAID levels are RAID 5 and RAID 10. Both provide fault tolerance through a different approach. Understanding the differences between these two RAID levels can help determine which one is best suited for a particular storage need.
Quick Answers
RAID 5 combines block-level striping with distributed parity. This means the data is striped across all the disks in the array, providing high performance. Parity information is also distributed across the disks, allowing the array to tolerate the failure of one disk drive. If a disk fails, the parity blocks on the remaining disks can be used to reconstruct the missing data.
RAID 10 combines mirroring and striping. Data is mirrored onto two identical drives, providing redundancy. Those mirrored pairs are then striped across multiple drive pairs, improving performance. RAID 10 can tolerate multiple drive failures so long as no more than one drive in a mirrored pair fails.
What is RAID 5?
RAID 5 is a widely used RAID level that provides a good balance of performance, capacity and fault tolerance. Here’s a quick overview of how RAID 5 works:
- Data is striped across all the disks in the array in blocks.
- Parity information is calculated and written across the disks.
- If any single disk fails, the parity blocks on the remaining disks can reconstruct the missing data.
- RAID 5 requires a minimum of 3 disks.
The distribution of parity information is the key to RAID 5’s fault tolerance. The parity blocks are staggered across all the disks. If any disk fails, the parity blocks on the other drives can be used to calculate the missing data.
For example, in a 3-disk RAID 5 array, Disk 1 may contain parity blocks 1, 4, 7, etc. Disk 2 contains parity blocks 2, 5, 8, and so on. This staggered layout allows RAID 5 to tolerate the loss of any one disk.
Advantages of RAID 5
- Good read performance – data is striped across multiple disks.
- Low cost – only requires a minimum of 3 disks.
- Can survive a single disk failure without data loss.
- Capacity utilization is good – equivalent to 1 disk worth of capacity lost for parity.
Disadvantages of RAID 5
- Slow write performance – parity must be calculated on every write.
- Array is vulnerable during disk rebuild after a failure.
- Poor performance with large capacity drives or heavy write workloads.
What is RAID 10?
RAID 10 combines both mirroring and striping for enhanced performance and fault tolerance:
- Data is mirrored onto two identical drives, providing redundancy.
- Those mirrored pairs are then striped across multiple drive pairs.
- RAID 10 requires a minimum of 4 disks (in 2 mirrored pairs).
This layout delivers fast performance by striping across drives, while also providing fault tolerance through mirroring. RAID 10 can withstand multiple drive failures so long as no more than 1 drive in a mirrored pair fails.
Advantages of RAID 10
- High read and write performance – mirroring and striping combine.
- Can withstand multiple drive failures (in separate mirrored pairs).
- Ideal for transactional workloads (databases, etc).
Disadvantages of RAID 10
- Higher hardware cost – requires at least 4 drives.
- Capacity utilization is only 50% since data is mirrored.
RAID 5 vs RAID 10: Key Differences
Here are some key differences between RAID 5 and RAID 10 at a glance:
| RAID 5 | RAID 10 |
|---|---|
| Distributed parity for redundancy | Mirroring for redundancy |
| Minimum 3 disks | Minimum 4 disks (in pairs) |
| High read performance | High read & write performance |
| Slow writes due to parity | Fast writes since no parity calc |
| Vulnerable during rebuilds | Can sustain multiple drive failures |
| Capacity utilization = N-1 disks | Capacity utilization = 50% only |
In summary:
- RAID 5 provides good performance and efficient use of capacity but has slower write speeds.
- RAID 10 delivers maximum performance and redundancy but uses capacity less efficiently.
When to Use RAID 5 vs RAID 10
So when should you choose one RAID level over the other? Here are some general guidelines:
Use RAID 5 if:
- You need a balance of performance, capacity and fault tolerance.
- Your workload is more read intensive than write intensive.
- You want efficient use of capacity from smaller number of drives.
- Your data is less mission critical where some downtime is acceptable.
Use RAID 10 if:
- Maximum performance and redundancy is critical.
- Your workload has a high proportion of writes.
- Fast fault tolerance is needed for critical data.
- Downtime must be minimized at all costs.
RAID 10 works best for mission critical systems where performance and high availability are top priorities. The extra hardware cost is justified for these types of applications.
RAID 5 offers strong fault tolerance at a lower hardware cost point. It fits well in environments where absolute maximum performance and uptime are less critical.
RAID Combinations
RAID 5 and RAID 10 can also be combined to get the best of both worlds:
RAID 50
RAID 50 combines the distributed parity of RAID 5 with the striping of RAID 0. It provides high performance while also supporting multiple drive failures.
- RAID 50 stripes RAID 5 sets together for enhanced performance.
- Can withstand multiple drive failures so long as each failure is on a separate RAID 5 set.
RAID 10+0
RAID 10+0 is nesting RAID 10 inside larger RAID 0 arrays. This provides performance acceleration from striping across multiple RAID 10 sets.
- Built by first creating RAID 10 mirror/stripe sets.
- Those RAID 10 sets are then striped using RAID 0 for higher performance.
- Can support multiple drive failures across different mirrored sets.
Software vs Hardware RAID
RAID can be implemented through dedicated hardware RAID controllers or through software in the operating system. Both have their pros and cons:
Hardware RAID
- Provides full RAID management in dedicated controller.
- Does not consume host system resources.
- Typically offers higher performance.
- More expensive, less flexible.
Software RAID
- Implemented through OS drivers and tools.
- Uses system CPU, memory and storage bus.
- Typically lower cost, more flexible.
- Performance limited by system resources.
Software RAID provides a low cost option using existing system resources. Hardware RAID delivers better performance and offloads RAID processing but at a higher price.
Conclusion
RAID 5 and RAID 10 offer two different approaches to RAID fault tolerance. RAID 5 uses distributed parity to efficiently provide redundancy for drive failures. RAID 10 duplicates data through mirroring for enhanced performance and redundancy.
RAID 5 is ideal for read intensive workloads that require a balance of performance and efficient storage capacity. RAID 10 works best for mission critical applications where maximum performance and redundancy is essential.
By understanding the core differences between these RAID levels, administrators can determine which technology best meets the speed, capacity and availability needs of a given environment.