What is Software RAID?

September 29, 2023

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RAID is a data storage technology that combines multiple physical drives into a single logical unit to enhance performance, reliability, and redundancy. It improves fault tolerance by distributing data across different disks, ensuring that if one drive fails, the data can still be recovered from others.

What is Software RAID?

Software RAID is a storage technology that organizes multiple physical drives into a single array using software rather than dedicated hardware. It enhances speed, storage capacity, and data safety by relying on the host system’s CPU and memory for RAID operations. Unlike hardware RAID, which uses dedicated controllers, software RAID eliminates the need for specialized hardware, reducing costs and increasing scalability. It’s relatively easy to set up, modify, and scale according to changing storage needs.

With the evolution of software-defined solutions, software RAID has emerged as a cost-effective, flexible alternative to traditional hardware RAID systems. In this article, we’ll explore the fundamentals of software RAID, its benefits, and provide several examples.

Understanding Software RAID

RAID technology improves performance and data redundancy by distributing data across multiple drives using techniques like striping, mirroring, and parity calculations. Popular RAID configurations, including RAID 0, 1, 5, 6, and 10, meet different needs ranging from speed to fault tolerance. It offers numerous advantages, such as high performance, data protection, and scalability making it essential for modern storage. Learn more about RAID levels in our guide: RAID Levels Explained, or explore the pros and cons in: Advantages and Disadvantages of RAID.

Both software and hardware RAID improve storage performance and reliability, but however, they differ in implementation and use cases.

  • Cost: Software RAID is more affordable, because it utilizes existing system resources instead of specialized hardware.
  • Flexibility: Software RAID is compatible with diverse storage configurations, including mixed drives and network storage like NVMe-oF. Hardware RAID, by contrast, is constrained by hardware-specific compatibility.
  • Performance: Historically, hardware RAID offered superior performance. However, modern software RAID solutions outperform traditional hardware RAID, particularly in environments leveraging NVMe drives.

To explore the benefits of software RAID in detail, check out our guide: Software RAID vs. Hardware RAID.

Another solution software RAID is traditionally compared to is erasure coding. RAID and erasure coding represent two powerful approaches to data protection, but they work differently. RAID prioritizes speed and redundancy, making it ideal for high-performance environments. On the other hand, erasure coding excels in storage efficiency and resilience, especially for distributed, cloud-scale applications.

Interestingly, RAID can be seen as a form of erasure coding, as it uses similar principles to manage data and parity. Advanced software RAID solutions, such as xiRAID, further elevate these technologies by offering high-speed, resource-efficient alternatives to both traditional RAID setups and erasure coding systems. For more on this comparison, explore the differences in our blog: RAID vs. Erasure Coding: What’s the Difference?

Popular Software RAID Solutions

1. mdraid (mdadm)

The mdadm tool, often referred to as mdraid, is the standard RAID management utility on Linux. It provides flexible configuration options and is widely supported across distributions. However, its performance is often insufficient for modern high-performance workloads, particularly when dealing with NVMe drives or applications requiring high sequential I/O.

2. Intel VROC (Virtual RAID on CPU)

Intel VROC is a hardware-assisted RAID solution leveraging Intel CPUs. It is tightly integrated with Intel platforms and supports NVMe RAID configurations without additional hardware RAID controllers. While it provides strong performance in supported environments, its Intel-specific nature limits its use to compatible platforms, and performance varies with workload complexity.

3. RAIDZ

RAIDZ, a part of the ZFS ecosystem, offers robust data integrity features like checksums and protection against silent data corruption. Its advanced architecture is a popular choice for environments prioritizing data safety. While its scalability makes it a favorite for data-heavy environments, its parity calculations can reduce performance in sequential or large-scale setups. For a deep dive into ZFS tuning and its limitations, check out our blog post: Tuning ZFS and Testing xiRAID as a Replacement for RAIDZ.

4. xiRAID

xiRAID is a high-performance software RAID solution designed to overcome the limitations of traditional RAID systems while ensuring robust data protection. Optimized for NVMe storage, it caters to modern workloads such as AI training, video editing, scientific simulations, and virtualized environments. xiRAID is provided in two versions: kernel-based xiRAID Classic and xiRAID Opus operating in user space which helps to bypass the kernel limits. xiRAID provides unparalleled flexibility by supporting block devices local or remote via PCIe, NVMe-oF, SPDK target, Fibre Channel, or InfiniBand. It exposes RAID arrays as a local block device, making it easy to integrate into existing systems.

Popular Software RAID Solutions - xiRAID

In collaboration with Kioxia, xiRAID has achieved record-breaking sequential I/O performance with PCIe Gen5 drives. By leveraging a lightweight architecture, xiRAID minimizes CPU overhead, requiring less than 10% CPU usage even under peak workloads, and maintains a low memory footprint of less than 4GB. This allows applications to maximize hardware resource utilization.

Comparison to other software RAID solutions:

  • When compared to VROC, xiRAID consistently outperforms it in terms of both read and write throughput as seen in a recent whitepaper by Western Digital. Benchmarking against Intel VROC for RAID5, xiRAID demonstrated a 128% improvement in sequential write performance and an 8% gain in sequential reads. Full details are available in the solution brief: read the whitepaper.
  • Compared to RAIDZ, xiRAID delivers up to 2x performance improvements in sequential workloads by bypassing some of the overhead associated with ZFS RAID configurations. Explore the technical details.
  • When tested in high-performance virtual environments with Kioxia PCIe Gen5 drives, xiRAID showcased substantial advantages over mdraid, mdraid struggled to fully utilize the potential of NVMe storage due to its older architecture, while xiRAID maximized throughput and significantly reduced latency. For further details, check out our blog on High-Performance Storage Solutions.

What sets xiRAID Apart:

  • Works across platforms and workloads without vendor lock-in.
  • Optimized for NVMe storage, achieving close to raw backend performance.
  • Lightweight design reduces CPU overhead, enabling better resource allocation for applications.

Conclusion

Software RAID is more than just a cost-saving alternative to hardware RAID. It's a transformative technology reshaping modern storage. By understanding its advantages and limitations, as well as comparing options like mdraid, RAID-Z, and xiRAID, businesses can make informed decisions to optimize their data infrastructure.