RAID (Redundant Array of Independent Disks) is a data storage technology that combines multiple disk drives to deliver increased performance, capacity, and reliability. There are several RAID "levels" with different mechanisms for distributing and duplicating data across drives. Two of the most popular configurations are RAID 5 and RAID 10. This article will compare and contrast these RAID levels to help IT professionals pick the right option for their needs.
What is RAID?
RAID combines multiple physical disk drives and uses software and techniques like mirroring, striping, and parity to achieve three key goals:
- Improve performance – distributing I/O across drives
- Prevent data loss – duplicating or recovering data
- Increase storage capacity
There are tradeoffs involved in optimizing for one factor over the others. Common RAID levels include:
- RAID 0 – Striping for pure performance
- RAID 1 – Mirroring for reliability
- RAID 5 – Striping with distributed parity for storage efficiency
- RAID 10 – Combination of mirroring and striping for performance/reliability
This article will focus on a detailed comparison of RAID 5 versus RAID 10.
How RAID 5 Works
RAID 5 requires a minimum of 3 disk drives. It works by breaking data into blocks which get distributed across all the drives in the array. Parity information is also calculated and written across the drives.
For example, with a 3-drive RAID 5 array:
- Drive 1 contains blocks A1, B2, C3
- Drive 2 contains blocks A2, B1 and the parity for block C1+C2+C3
- Drive 3 contains blocks A3, B3 and the parity for block A1+A2+A3
If any single drive fails, the array can reconstruct all the data using the information remaining on the other drives. This provides fault tolerance with good overall storage efficiency. However, write performance suffers due to parity calculation overhead.
Additional RAID 5 architectures are possible for improved performance or redundancy:
- RAID 5 + Hot Spare – Adds dedicated standby drive that can automatically rebuild failed disk
- RAID 6 – Double distributed parity provides protection against 2 disk failures
RAID 5 Rebuild Process
When an individual drive fails in a RAID 5 array, a rebuild must take place to restore redundancy and fault tolerance. This involves:
- Replacing the failed physical drive
- Reading all data from surviving disks
- Recalculating missing data using parity info
- Writing the rebuilt data to the new replacement drive
For large capacity disk arrays, this rebuild process can take many hours depending on the drive technology involved:
| Drive Type | Size | Rebuild Time |
|---|---|---|
| HDD – 15K RPM | 900 GB | 4-6 hours |
| SSD – Entry Enterprise | 1.6 TB | 3-4 hours |
| HDD – 7.2K RPM | 10 TB | 15+ hours |
During the rebuild, application performance can be 20-50% lower depending on load levels. For mission critical systems, the storage penalty and extended vulnerability window can be too risky for RAID 5.
Advantages of RAID 5
- Good storage efficiency – total capacity is size of drives * (n-1)
- No mirroring required compared to RAID 1
- Data remains available and can be rebuilt if single drive fails
- Supported by most RAID controllers – easy to implement
Disadvantages of RAID 5
- Write performance impacted due to parity calculation (30-50% slower)
- Total failure results if second drive fails before rebuild
- Rebuild times can be very long with larger drives
- Degraded performance during rebuilds
- Susceptible to latent sector errors going undetected
How RAID 10 Works
RAID 10 requires a minimum of 4 disk drives and combines both striping for performance and mirroring for fault tolerance. Here‘s how it works:
- Data is striped across drives similarly to RAID 0
- A mirrored copy of each stripe set is made on additional drives
For example, with a 4-drive RAID 10 configuration:
- Drives 1 & 2 contain striped data A1, B1, C1
- Drives 3 & 4 contain the mirror copies A2, B2, C2
This duplication protects against drive failures, while the striping distributes read/write load evenly across drives. RAID 10 works best with matched drive pairs. Larger arrays can improve performance but with higher cost.
RAID 10 Rebuild Process
When a disk fails in a RAID 10 array, rebuilding the data simply involves placing a new replacement drive and remirroring. The rebuild performance penalty is minimal since no complex parity calculations are required. A sample rebuild process would be:
- Detect and confirm drive failure in mirrored pair
- Remove failed physical drive
- Insert blank replacement drive to logical slot
- Automatically remirror surviving drive to rebuild
Total rebuild windows range from 30 minutes to 2 hours even for large multi-terabyte drive sizes, with minimal performance impact. This allows RAID 10 to recover much quicker from failures than RAID 5.
Advantages of RAID 10
- Very high read and write performance from striping
- Fault tolerant – survives multiple drive failures
- Quick and low impact drive rebuilds
- Supported on most RAID controllers
Disadvantages of RAID 10
- 50% storage efficiency – drives are mirrored 1:1
- More expensive due to mirrored drives
- 4 drive minimum requirement
RAID 5 vs RAID 10 Comparison
Here is a direct side-by-side comparison of RAID 5 and RAID 10 based on several key factors:
| RAID 5 | RAID 10 | |
|---|---|---|
| Minimum Drives | 3 | 4 |
| Storage Efficiency | 60-70% | 50% |
| Rebuild Times | Longer | Faster |
| Fault Tolerance | Withstands 1 drive failure | Withstands 2+ drive failures |
| Read Performance | Good | Excellent |
| Write Performance | Poor due to parity | Excellent |
| Cost per TB | Lower | Higher |
As this comparison shows, RAID 10 has clear advantages when maximum performance and high availability are required. The tradeoff is much higher cost per terabyte due to the drive duplication. RAID 5 offers strong storage efficiency with some fault tolerance, but performance suffers due to parity and long rebuilds.
Drive Failure Rate Comparisons
Industry drive failure rate statistics also shed some light on the expected reliability of RAID 5 vs RAID 10 over time. Drives are rated by AFTR (Annualized Failure Rate):
| Drive Class | AFTR | MTBF |
|---|---|---|
| Enterprise HDD | 2-4% | 2.5 – 5 million hours |
| Enterprise SSD | 0.5 – 1 % | 10+ million hours |
Even with field failure rates of 1-2%, rebuild windows and performance impacts make RAID 5 high risk once array size grows. But for RAID 10, sub-1% SSD failure rates give high statistical reliability. This lets RAID 10 tolerate up to 2 drive failures with little capacity or performance penalty.
RAID 5 vs RAID 10 Performance
Differences in underlying technology also impact real world performance between these RAID types:
| RAID 5 | RAID 10 | |
|---|---|---|
| Max Throughput | 600 MB/sec | 1200 MB/sec |
| Max IOPS | 5,000 | 10,000+ |
| Latency | 5-10 ms | < 1 ms |
RAID 10 provides up to 2X throughput and 4X+ IOPS compared to RAID 5 with faster response times. This speed advantage comes from avoiding parity calculations on writes. The exact performance delta depends on application profiles, but RAID 10 is much higher across the board.
RAID 5 vs RAID 10: Usage Scenarios
Based on the comparisons in this guide, below are typical usage scenarios where each RAID level is ideally suited:
RAID 5 Ideal Usage
- File servers and backup storage
- Write-heavy environments without parity bottlenecks
- General purpose applications focused on storage density
RAID 10 Ideal Usage
- Transactional databases (OLTP) requiring fast response
- High performance computing data storage
- Business critical applications where uptime is imperative
- I/O intensive virtualized server workloads
- Analytics platforms demanding faster time-to-insight
For a real world RAID 10 usage example, a 100TB OLTP SQL Server database broken into 10x 1TB datastores would benefit greatly. Mirrored 15K HDD RAID 10 sets would prevent storage bottlenecks during peak transaction times. And 500GB SSD RAID 10 volumes take this performance advantage even further.
RAID 5 vs RAID 10 Cost Comparison
While performance and reliability considerations are foremost, budget restrictions can dictate choices between RAID levels. Below is a sample cost analysis for a 6 drive array with 4TB enterprise SATA drives:
| Configuration | Drives | Raw Capacity | Useable Capacity | Cost |
|---|---|---|---|---|
| RAID 10 | 6 | 24 TB | 12 TB | $4,500 |
| RAID 5 | 6 | 24 TB | 20 TB | $3,750 |
With a 67% bump in price but 2X+ gains in performance and redundancy, RAID 10 delivers tangible advantages for mission critical data availability. RAID 5 offers a more economical choice for general purpose storage.
Software vs Hardware RAID
Aside from RAID levels, storage can also be implemented via:
- Software RAID – OS and server CPU manage the array
- Hardware RAID – Processing offloaded to RAID card
Hardware RAID advantages include better performance, battery-protected cache, and less CPU overhead. But software RAID offers flexibility and avoids vendor lock-in. For RAID 5/10, hardware RAID and BBU caching smooth performance edges compared to software RAID implementations.
The Bottom Line
While both provide increased data availability, RAID 5 and RAID 10 get there via very different methods. RAID 5 economizes capacity with parity striping but RAID 10 mirrors striped data for pure speed. Ultimately RAID 10 is the gold standard for applications where uptime SLAs and fast transaction response are critical enough to warrant the premium expense. RAID 5 hits a flexible sweet spot blending capacity, efficiency and rebuild times for more general data storage needs.