When setting up a RAID configuration with only 2 drives, the two main options to provide redundancy are RAID 1 and RAID 0+1. RAID 1, also known as disk mirroring, is generally considered the best option for a 2 drive system if redundancy is the priority.
What is RAID 1?
RAID 1 creates an exact copy (or mirror) of one drive to another drive. This means the two drives contain the exact same data. If one drive fails, the system can instantly switch to the other drive without any data loss or service interruption. The usable storage capacity in a 2 drive RAID 1 configuration is equal to the capacity of a single drive. For example, two 1TB drives configured in RAID 1 would provide 1TB of usable storage.
The key benefits of RAID 1 with 2 drives include:
- Very simple to setup and manage
- Provides complete data redundancy – if one drive fails the other is an exact copy
- Read performance is better than a single drive as reads can be distributed across both drives
- Rebuild after a drive failure is faster than more complex RAID setups
The main limitations with 2 drive RAID 1 are:
- 50% storage efficiency – the usable capacity is only equal to one drive
- No read/write performance improvement compared to a single drive
- Does not protect against file corruption or accidental deletion
What is RAID 0+1?
RAID 0+1 is also known as RAID 10 and combines both RAID 0 striping and RAID 1 mirroring. With 2 drives, RAID 0+1 works by first mirroring each individual drive (RAID 1), and then striping data across the mirrored sets (RAID 0). This provides both data redundancy from RAID 1 and some performance benefits from RAID 0 striping.
The key benefits of RAID 0+1 with 2 drives include:
- Strong data redundancy from the RAID 1 mirroring
- Slightly better read performance than a single drive
- Usable capacity is equal to one drive, same as RAID 1
The main limitations are:
- More complex to setup and manage than RAID 1
- No write performance improvement over a single drive
- Rebuild after a drive failure takes longer than RAID 1
- Still only 50% storage efficiency
Comparing RAID 1 vs RAID 0+1 with 2 Drives
When considering RAID 1 vs RAID 0+1 in a 2 drive configuration, RAID 1 generally provides the better combination of data redundancy, performance, and simplicity:
| Factor | RAID 1 | RAID 0+1 |
|---|---|---|
| Data redundancy | Excellent – complete mirroring | Excellent – mirrored stripes |
| Read performance | Good – reads split between drives | Slightly better – striping improves distribution |
| Write performance | Same as single drive | Same as single drive |
| Storage efficiency | 50% – capacity of 1 drive | 50% – capacity of 1 drive |
| Rebuild time | Very fast | Slower than RAID 1 |
| Complexity | Very simple | More complex than RAID 1 |
As the table summarizes, both RAID 1 and RAID 0+1 provide excellent redundancy for 2 drive systems. But RAID 1 is simpler to setup and manage, provides faster rebuilds, and is more efficient for small setups like 2 drives. For these reasons, RAID 1 is generally considered the preferred solution for maximizing redundancy with only 2 drives.
Real-World Performance Expectations
When estimating real-world read/write performance with RAID 1 versus a single drive, some approximate benchmarks are:
- Sequential Read Speed: Up to 2x faster than a single drive
- Random Read Speed: Up to 50% faster than a single drive
- Sequential Write Speed: Similar to a single drive
- Random Write Speed: Similar to a single drive
So while RAID 1 does provide a noticeable gain for read-intensive workloads, for general mixed use its write performance remains similar to a single disk. RAID 0+1 may provide slightly better read performance due to the additional striping, but the gains are marginal with only two drives.
When is RAID 0+1 Preferable to RAID 1?
The one scenario where RAID 0+1 may be preferable to RAID 1 with 2 drives is when consistently very high read performance is required. The striping in RAID 0+1 can provide additional read performance gains compared to RAID 1 mirroring alone. However, the performance difference is generally not significant with only two drives.
Once more than 2 drives are used, RAID 0+1 becomes much more beneficial compared to RAID 1. The striping provides better read/write distribution across the larger array. But for most purposes with only 2 disks, RAID 1 offers the best combination of redundancy, performance and simplicity.
Choosing the Right Drives for 2 Drive RAID
The specific drives chosen for a 2 disk RAID configuration can impact reliability and performance. Here are some tips for choosing drives:
- Use enterprise or NAS rated drives designed for 24/7 operation
- Select drives from the same batch/model for consistency
- Use drives of the same capacity to better balance storage use
- Consider drives with vibration sensors for early failure detection
- Favor 7200RPM or high RPM drives to improve performance
For home or small office use, a pair of quality consumer grade NAS drives from reputable brands like WD Red or Seagate IronWolf are good options. For more demanding environments, enterprise class SAS or SATA drives provide better sustained performance and longevity.
RAID Controller and Software Considerations
To access the full features and reliability of RAID, a dedicated hardware or software RAID controller is recommended. The controller manages the RAID configuration, drive monitoring, background data integrity checks, and rebuilding failed drives.
Hardware RAID controllers provide the best performance and availability. But software RAID through Windows, Linux, or a NAS OS can also work well for home or small business use. The RAID management software should include drive health monitoring and alert notifications to detect problems early.
Drawbacks of RAID as Sole Backup
While RAID provides redundancy against drive failures, it does not protect against other scenarios like:
- Disasters that damage multiple drives
- Accidental file deletion or corruption
- Malware, viruses, or ransomware
- Hardware failures affecting the RAID controller or server
To fully protect business critical data, RAID should be combined with backups to an external location or cloud service. Regularly test restoring from backups to validate their integrity.
Alternatives to Consider
Although RAID 1 is the typical solution for a 2 drive redundant array, alternatives to consider include:
- ZFS Mirror – modern mirrored pool option with more flexibility and features than RAID 1
- Storage Spaces – Microsoft’s software-defined storage with mirroring support
- Drobo – uses proprietary BeyondRAID technology for simplified data protection
Each option has pros and cons to weigh based on your specific use case and requirements.
Conclusion
For a 2 disk redundant array, RAID 1 mirroring provides the best combination of performance, protection, and simplicity. It is easy to setup while providing complete data redundancy. RAID 0+1 offers only marginal additional performance gains in a 2 drive configuration. To fully protect business data, RAID should be combined with external backups and disaster recovery preparations.
