Quick Answer
No, all drives do not have to be the same for RAID 10. RAID 10 can utilize drives of different sizes and speeds. However, performance and storage capacity will be limited by the smallest and slowest drives. Using identical drives is recommended for optimal performance.
What is RAID 10?
RAID 10, also known as RAID 1+0, is a hybrid RAID level that combines disk mirroring and disk striping to provide redundancy and improved performance. In RAID 10, data is mirrored across pairs of drives, while these mirrored pairs are then striped across multiple drive pairs.
This configuration provides fault tolerance and fast read/write speeds. If one drive in a mirrored pair fails, the system can instantly failover to the other disk without any data loss. The striping across mirrored pairs allows for parallel data access, enhancing performance.
RAID 10 Drive Requirements
Unlike other RAID levels, RAID 10 does not require all disks to be identical in terms of size or speed. However, there are some general guidelines to follow:
Number of Drives
RAID 10 requires a minimum of 4 drives to provide data redundancy. The drives need to be configured as mirrored pairs, so there must be an even number of disks. Most implementations utilize 4, 6, 8, or 10 drives.
Drive Capacity
Drives of different sizes can be combined in a RAID 10 array. However, drive capacity will be limited to the size of the smallest disk. For example, combining a 500 GB and 1 TB drive would result in 500 GB of usable storage.
Drive Speed
Faster and slower drives can co-exist in the same RAID 10 configuration. But performance will be dictated by the speed of the slowest drive. Mixing 7200 RPM and 10,000 RPM drives will lower performance versus using all 10,000 RPM drives.
Drive Interface
All drives in a single RAID 10 array should use the same interface, such as SATA, SAS, or NVMe. Mixing drive interfaces is not recommended and can cause compatibility issues.
Benefits of Using Identical Drives
While RAID 10 does offer flexibility with drive selection, using identical drives comes with advantages:
Maximized Capacity
With identical drives, you can take full advantage of the combined storage capacity. Arrays with mixed drive sizes will have capacity limited by the smallest disk.
Optimized Performance
Identical drives with the same rotational speed allow for balanced performance across all disks. There is no slow drive holding back the faster drives.
Simplified Management
Standardizing on one drive model and firmware version can make maintenance and monitoring easier compared to managing an array of mixed drives.
Cleaner Failures
Should a drive fail, replacing it with the same model ensures consistency across the rebuilt RAID 10 array. Rebuilding with a different drive introduces variability.
Examples of Mixed RAID 10 Configurations
Some example scenarios when heterogeneous drives can be combined in RAID 10:
Short-Term Cost Savings
Use smaller, slower leftover drives along with new high-capacity drives to save money upfront. Replace old drives with new models over time.
Transition to Larger Drives
When transitioning to larger drives, introduce new drives into the RAID 10 array gradually rather than all at once. This allows you to spread out the cost over time.
Combining SSDs and HDDs
Use SSDs for improved performance and HDDs for larger capacity at a lower cost. The SSDs can handle key workloads while HDDs store less frequently accessed data.
| Drive Type | Number of Drives | Drive Capacity | Total Capacity |
|---|---|---|---|
| 2x SSD | 2x 128GB | 256GB | |
| 4x HDD | 4x 2TB | 4TB | |
| Total | 6 | 4.25TB |
Drawbacks of Mixing Drives
Using drives of different sizes, speeds, and models in RAID 10 can introduce some potential setbacks:
Compromised Performance
Performance bottlenecks can occur when faster drives are slowed down by older, slower models. This negates some of the speed benefits of RAID 10.
Added Complexity
Additional monitoring and attentiveness is required to track arrays with mixed drive models versus those with identical models. Firmware differences can also cause issues.
Rebuilding Challenges
Rebuilding the array after a drive failure can be problematic if you do not replace with an identical disk. The new drive becomes the “odd one out”.
Difficult Capacity Planning
With mixed drive sizes, total usable capacity can be confusing and less straightforward to plan out. Wasted space on larger drives makes optimization more difficult.
RAID Controller Support
The RAID controller used will also impact your ability to mix and match drives. Some controllers are more flexible, while others have tighter requirements:
Hardware RAID
Most hardware RAID controllers allow mixing drives of different sizes and speeds to some degree. However, performance is still dependent on the attributes of the underlying physical disks.
Software RAID
Linux software RAID and Windows Storage Spaces support combining heterogeneous physical drives into a virtual RAID 10 array. This provides more flexibility compared to hardware RAID.
ZFS and MDADM
Open source RAID implementations like ZFS and MDADM on Linux have native support for creating RAID 10 arrays from drives of varying sizes and speeds.
Recommendations for Mixed RAID 10 Arrays
If you do opt to combine different drive models in RAID 10 configuration, here are some best practices:
Match Capacities
Group drives of similar sizes together when creating mirrored pairs to avoid wasting disk space.
Segregate Performance
Keep slower HDDs in separate mirrored sets from SSDs or faster HDDs to optimize performance.
Consider Workloads
Place highly read/write intensive application data on faster SSDs. Use slower HDDs for bulk storage.
Monitor Health
Watch for signs of impending drive failure more closely to avoid rebuilding with different models.
Standardize Where Possible
Use the same size, speed and type for at least some of the drives. For example, use 2 pairs of 1TB SSDs along with 2 legacy HDDs.
Conclusion
While RAID 10 provides flexibility to combine different drive types, capacities and speeds, there are tradeoffs in overall performance, usable capacity and ease of management. Using identical drives is still the ideal scenario for RAID 10 deployments when possible. However, mixing drives can be a temporary solution when transitioning arrays over time. Careful planning and testing is required to ensure stability and meet performance requirements when utilizing heterogeneous drives.