RAID 0 1, also known as RAID 10 or RAID 1+0, is a hybrid RAID configuration that combines disk striping and disk mirroring to provide increased performance and fault tolerance compared to other RAID levels. In RAID 0 1, data is striped across multiple drives like in RAID 0, but the striped sets are also mirrored like in RAID 1.
What does RAID stand for?
RAID stands for Redundant Array of Independent Disks. It is a data storage technology that combines multiple disk drives into a logical unit to provide increased storage capacity, reliability, and performance. The different RAID levels use various techniques like striping, mirroring, and parity to achieve different optimizations.
What is disk striping in RAID 0 1?
Disk striping is the technique used in RAID 0 1 where data is split into blocks and written across multiple drives in the array simultaneously. This allows for parallelization which improves performance and bandwidth since multiple drives are accessed at once instead of just one.
In RAID 0 1, disk striping is achieved by combining two or more RAID 0 disk arrays into a single array. Data is striped across each RAID 0 array, providing performance benefits from the striping.
What is disk mirroring in RAID 0 1?
Disk mirroring is the technique used in RAID 0 1 where identical copies of data are maintained on duplicate sets of drives. This provides fault tolerance by allowing seamless failover to the mirrored copy if one drive fails.
In RAID 0 1, the striped RAID 0 arrays themselves are mirrored. So if a drive in one RAID 0 array fails, the corresponding mirrored drive in the other RAID 0 array can continue servicing data requests without interruption. This combines the performance of RAID 0 striping with the fault tolerance of RAID 1 mirroring.
How does RAID 0 1 combine RAID 0 and RAID 1?
RAID 0 1 combines disk striping from RAID 0 and disk mirroring from RAID 1 for increased performance and fault tolerance:
- Data is striped across multiple drives like in RAID 0, providing performance benefits from parallelization.
- The RAID 0 arrays are mirrored like in RAID 1, providing fault tolerance through redundancy.
- If one disk in a RAID 0 array fails, the mirror in the other array continues service.
- RAID 0 style striping provides speed, while RAID 1 style mirroring provides reliability.
What are the benefits of RAID 0 1?
Some key benefits of RAID 0 1 include:
- Increased read/write performance – Disk striping allows for fast parallel reads and writes across multiple drives.
- Fault tolerance – Disk mirroring provides redundancy for failover in case of drive failure.
- Improved bandwidth – Spreading data across multiple disks improves overall array bandwidth.
- Minimized rebuild times – Only failed stripes need to be rebuilt after drive failure.
What are the drawbacks of RAID 0 1?
Some potential drawbacks of RAID 0 1 include:
- Higher cost – Requires at least 4 drives to implement minimum 2 drive mirrors.
- Overhead – Computing parity adds processing overhead.
- Lower capacity utilization – Effective capacity is 50% due to mirroring inefficiency.
- Read performance overhead – Both disks in a mirror must be read during reads.
When should you use RAID 0 1?
Here are some good use cases for implementing RAID 0 1:
- When high performance is the priority for read and write intensive applications.
- When high availability and fault tolerance is critical.
- For database servers that require fast I/O performance.
- For virtualized environments to minimize downtime from drive failures.
- For mission critical systems that need both speed and reliability.
Minimum number of drives for RAID 0 1
The minimum number of drives required to implement RAID 0 1 is 4 drives:
- 2 drives for first RAID 0 stripe set
- 2 drives for second RAID 0 stripe set to mirror first set
With just 2 drives, you can implement RAID 0 striping or RAID 1 mirroring, but not the hybrid RAID 0 1.
Drive failure scenarios in RAID 0 1
Here are the scenarios for RAID 0 1 when drive failures occur:
- If 1 drive fails, there is no data loss since the mirror drive takes over. Performance degrades to RAID 0 speeds until failed drive is replaced.
- If 2 drives fail in the same mirrored set, there is complete data loss for that RAID 0 array. The full RAID 0 1 array fails.
- If 1 drive fails in each mirrored set, performance degrades but there is no data loss. Reads must go to both arrays.
- If more than 2 drives total fail, there is complete data loss for the RAID 0 1 array.
RAID 0 1 capacity calculations
Total usable capacity in a RAID 0 1 array can be calculated as:
- Number of RAID 0 arrays = Total drives / Drives per RAID 0
- Capacity of each RAID 0 = Smallest drive size * Drives per RAID 0
- Total capacity = Capacity of one RAID 0 * Number of RAID 0 arrays
For example, with 4 x 2TB drives:
- 2 RAID 0 arrays with 2 drives each
- Each RAID 0 capacity = 2TB * 2 drives = 4TB
- Total capacity = 4TB * 2 RAID 0 arrays = 8TB
So for 4 x 2TB drives, the total usable RAID 0 1 capacity is 8TB.
Comparison between RAID 0 1 vs RAID 1 0
RAID 0 1 and RAID 1 0 are essentially equivalent, but there are some subtle differences:
| RAID 0 1 | RAID 1 0 |
|---|---|
| Stripe sets mirrored | Mirrors striped |
| Write performance focused | Read performance focused |
| Mirrored stripes aid sequential writes | Striped mirrors aid parallel reads |
In most cases, RAID 0 1 and RAID 1 0 can be used interchangeably based on vendor implementation.
Verifying RAID 0 1 in Linux
In Linux, RAID 0 1 arrays can be verified using the following commands:
cat /proc/mdstat– Check current RAID arrays and statusmdadm --detail /dev/mdX– Show details of RAID array /dev/mdXgrep mdX /proc/partitions– Verify devices mapped to /dev/mdX array
The mdadm detail output will indicate RAID level as raid10 for a RAID 0 1 array.
Conclusion
RAID 0 1 combines performance and fault tolerance by striping and mirroring drives. It requires at least 4 drives and provides speed benefits from RAID 0 striping along with redundancy from RAID 1 mirroring. RAID 0 1 is ideal for high throughput scenarios that also demand high availability like databases and virtualized environments. While more expensive than standalone RAID 0 or RAID 1, RAID 0 1 offers the best of both worlds for critical data storage needs.
