TL;DR
It is technically possible to run RAID 0 and RAID 1 on the same set of drives simultaneously, but it is not recommended and requires special hardware/software configurations. The benefits of doing so are limited and it adds complexity. It is better to choose one RAID level or the other depending on your needs for performance vs. fault tolerance.
What is RAID?
RAID stands for Redundant Array of Independent Disks. It is a way of combining multiple physical disk drives into a single logical unit to provide increased performance, capacity, and/or reliability compared to a single drive.
There are several different RAID levels, each with its own mix of benefits and drawbacks:
RAID 0
RAID 0 stripes data across multiple disks with no redundancy. It provides improved performance since reads/writes are distributed across drives, but there is no fault tolerance – if one drive fails, all data is lost.
RAID 1
RAID 1 mirrors data between two or more disks. This provides full redundancy – if one drive fails, data can be rebuilt from the other mirror drive(s). But usable capacity is only equal to one drive.
RAID 5
RAID 5 stripes data across drives like RAID 0, but also provides parity information so that data can be rebuilt if a single drive fails. Capacity is equal to the size of all drives minus one.
RAID 6
RAID 6 is similar to RAID 5, but uses a second distributed parity scheme to allow data recovery in the event of two drive failures. Capacity is equal to all drives minus two.
RAID 10
RAID 10 mirrors drives like RAID 1 while also striping data like RAID 0. This provides both performance and redundancy, but cuts the total capacity in half.
Benefits and Drawbacks of RAID 0 and RAID 1
RAID 0 Benefits
– Increased read/write performance by distributing I/O across drives
– Utilizes full combined capacity of drives
RAID 0 Drawbacks
– No fault tolerance – single drive failure results in total data loss
– Less reliable than a single drive
RAID 1 Benefits
– Full redundancy – data is replicated so it can survive a drive failure
– Increased read performance by reading copies simultaneously
RAID 1 Drawbacks
– Write performance limited to single drive speed
– Capacity is only equal to one drive
Is it Possible to Run RAID 0 and RAID 1 Together?
Technically, yes it is possible to run both RAID 0 and RAID 1 on the same set of physical disks. This requires a RAID controller and software that supports a multi-level or nested RAID configuration.
For example, with 4 drives:
– Drives 1 and 2 could be configured as a 2-disk RAID 0 stripe set
– Drives 3 and 4 could be configured as a 2-disk RAID 1 mirror
– The RAID 0 and RAID 1 sets could then be combined into a single RAID 0+1 array
This results in a configuration that mirrors data between the RAID 1 pair, while also striping/distributing reads/writes across the RAID 0 stripes.
Some enterprise-grade RAID controllers support concatenating multiple RAID levels like this. Consumer motherboards and software RAID implementations may not have this capability. The RAID controller or software have to explicitly support RAID 0+1 or similar nested RAID.
What are the Potential Benefits of RAID 0+1?
Combining RAID 0 striping with RAID 1 mirroring can provide some advantages compared to either separately:
– **Increased read performance** – Reads can be distributed across RAID 0 stripes and both disks in the RAID 1 mirrors.
– **Reduced risk of data loss** – RAID 1 mirroring provides redundancy if a drive fails. Data would be preserved in the mirror drive.
– **Faster rebuilds** – If a drive in the RAID 1 mirror fails, the rebuild time is faster since it only has to copy from the other mirror drive rather than recalculating parity.
However, the benefits are relatively minor compared to the downsides and complexity.
What are the Drawbacks of RAID 0+1?
There are some significant downsides to configuring RAID 0 and RAID 1 together:
– **Added complexity** – More complex to configure and manage. Potential for user error.
– **Extra overhead** – Computing parity and mirroring takes processing resources.
– **Lower total capacity** – Combining RAID 0 and RAID 1 effectively cuts the usable capacity in half compared to RAID 0 alone.
– **Write performance limited** – Writes are bottlenecked by single drive speed, unlike standalone RAID 0 configuration.
– **No additional redundancy** – Provides no more redundancy than RAID 1 alone already achieves.
– **Hardware support** – Requires RAID controller/software that specifically supports nested RAID levels.
For most use cases, the disadvantages outweigh the minor benefits. The performance gains are minimal, while capacity and simplicity suffer.
When Does RAID 0+1 Make Sense?
RAID 0+1 can be beneficial in certain niche scenarios:
– **Database servers** – Where read performance is critical. The redundancy of RAID 1 plus distributed reads of RAID 0 can improve database queries.
– **Small arrays** – RAID 0+1 can make sense with only 2-4 drives where drive sizes are already large. Capacity limitation is less impactful.
– **Business continuity** – If extremely high availability and minimum rebuild times are critical, the RAID 1 mirroring provides an advantage.
But for general file and application servers, standalone RAID 0 or RAID 1 usually makes more sense depending on your performance vs. redundancy needs.
Alternative RAID Configurations
Instead of combining RAID 0 and RAID 1, other RAID levels can provide different performance/redundancy tradeoffs:
RAID 10
RAID 10 provides a mirrored, striped array like RAID 0+1. But RAID 10 is implemented in the RAID controller itself rather than layered RAID 0 and RAID 1 sets.
RAID 5
RAID 5 provides striping with distributed parity, allowing for redundancy with minimal capacity loss. Rebuild times are slower than RAID 1 or RAID 10 though.
RAID 6
RAID 6 is like RAID 5 but with dual parity, allowing for up to two drive failures with only 2 drives loss in capacity.
RAID 50/60
Nested RAID levels like RAID 50 (RAID 5 striped arrays with RAID 0) or RAID 60 (RAID 6 striped with RAID 0) can provide redundancy while increasing performance through striping.
These may provide a better overall balance than combining RAID 0 and RAID 1 in most use cases. The exact optimal RAID type depends on your specific goals.
Software vs Hardware RAID
Running RAID 0+1 or other nested RAID levels requires RAID controllers that have this capability. Software RAID solutions may not support these more advanced configurations.
Hardware RAID cards provide maximum performance and advanced RAID capabilities. But they add cost compared to software RAID using the operating system or motherboard RAID support.
If you need features like nested RAID levels, booting from RAID, or maximum reliability, a dedicated hardware RAID controller is recommended.
How to Configure RAID 0+1
If you do want to configure nested RAID 0 and RAID 1 on a set of drives, the steps would include:
1. Check that your RAID controller/software supports RAID 0+1 or similar multi-level RAID.
2. Install matching drives of the desired size into the RAID controller ports.
3. Use the RAID controller BIOS/utility to:
– Create a 2-disk RAID 0 array from drives 1 and 2
– Create a 2-disk RAID 1 array from drives 3 and 4
– Combine the RAID 0 and RAID 1 sets into a single RAID 0+1 array
4. Initialize and format the RAID 0+1 array as a single volume.
5. Configure your operating system and mount the volume to begin using the storage.
The process can vary between different RAID controller brands – consult your vendor documentation for specifics.
Conclusion
While possible, running both RAID 0 striping and RAID 1 mirroring on the same physical disks provides minimal benefits for most use cases. The added complexity, capacity loss, and performance limitations usually make standalone RAID 0 or RAID 1 a better choice. Multi-level RAID configurations like RAID 10 or RAID 50 are preferable alternatives if you need both redundancy and performance. Make sure your RAID controller or software supports nested RAID levels before attempting to configure RAID 0 and RAID 1 on the same array.
