RAID (Redundant Array of Independent Disks) is a data storage technology that combines multiple disk drive components into a logical unit. RAID provides increased storage functions and reliability through redundancy. There are two main types of RAID implementations – hardware RAID and software RAID. While both provide benefits, hardware RAID is generally considered superior to software RAID.
What is RAID?
RAID is a technology that combines multiple physical disk drive components into one or more logical units for the purposes of data redundancy, performance improvement, or both. This is achieved by distributing data across the drives in one of several ways called “RAID levels.” Some key characteristics of RAID include:
- Combining multiple drives into a logical unit
- Data redundancy through mirroring or parity allowing recovery from drive failure
- Increased performance by distributing I/O across drives
The different RAID levels provide various combinations of increased data reliability and/or improved performance. The most commonly used RAID levels are:
| RAID Level | Description |
|---|---|
| RAID 0 | Disk striping without parity or mirroring. Provides improved performance but no redundancy. |
| RAID 1 | Disk mirroring without parity or striping. Provides redundancy but no performance gain. |
| RAID 5 | Block-level striping with distributed parity. Provides both redundancy and improved disk performance. |
RAID can be implemented via dedicated hardware RAID controllers or via software-based RAID built into operating systems and server software. The choice between hardware or software RAID depends on factors like cost, performance, features needed, and administrator preferences.
Hardware RAID Overview
Hardware RAID uses dedicated RAID controller cards that are installed in a server or computer. The RAID card handles all RAID calculations, parity, caching, and disk I/O optimization at the hardware level. Hardware RAID provides the following advantages:
- Better performance – Hardware RAID offloads processing overhead from the CPU allowing it to focus on other tasks. The RAID card’s dedicated processor and cache improves disk I/O and throughput.
- Increased reliability – If a drive fails, the RAID card is hardware-optimized to rebuild the drive and reestablish redundancy. System uptime and data integrity is maintained.
- Operating system independence – Hardware RAID works independently of the operating system and drivers. The RAID configuration and logical drives persist even during OS reinstalls or upgrades.
- Advanced feature set – Hardware RAID controllers offer extensive RAID options including nested RAID levels, online capacity expansion, and robust caching abilities.
Hardware RAID does have some downsides. It requires purchasing proprietary RAID cards that can be expensive compared to software RAID. The RAID card must be compatible with the motherboard which limits flexibility. If the RAID card fails, the entire system is at risk until replaced.
Software RAID Overview
Software RAID manages RAID at the operating system or software driver level instead of using dedicated hardware. Linux, Windows, and virtualization platforms like VMware have built-in software RAID capabilities. Key characteristics of software RAID include:
- Lower cost – Software RAID uses existing system hardware and doesn’t require purchasing RAID cards.
- OS and platform flexibility – Software RAID works across different operating systems and motherboards.
- Ease of management – Software RAID volumes can be configured and managed through familiar OS or virtualization tools.
However, software RAID does have some limitations compared to hardware RAID:
- Performance overhead – The system CPU has to handle RAID calculations and I/O processing which can reduce performance.
- Limited feature set – Software RAID usually has less extensive caching, rebuild, and volume management abilities compared to hardware RAID cards.
- OS dependency – The software RAID configuration is tied to the OS or platform. If the OS fails, the RAID volumes may be lost.
Hardware RAID Performance Advantages
One of the key advantages of hardware RAID over software RAID is better performance and throughput. Hardware RAID offloads the intensive parity calculations and I/O processing required by RAID from the main CPU onto the RAID card’s specialized storage processor. This provides several benefits:
- Frees CPU resources for running other applications and processes
- Allows CPU power to scale virtual machines and hosts without RAID bottlenecks
- Provides dedicated RAID cache that improves read and write speeds
- Optimizes disk I/O throughput via the RAID processor
Hardware RAID performance superiority over software RAID has been demonstrated in benchmarks and real-world configurations:
- Hardware RAID 0 delivers up to 20% higher throughput than software RAID 0 in 4K random read/write benchmarks.
- Software RAID 5 exhibits significantly lower transactional database performance than hardware RAID 5 due to CPU overload.
- Virtualized environments see dramatic improvements in VM density and reduced CPU usage with hardware vs. software RAID.
Software RAID can experience degraded performance because the main system CPU has to handle disk I/O in addition to other demands. Hardware RAID offloads these CPU-intensive storage tasks onto a dedicated RAID processor optimized for storage access and throughput.
Increased Reliability with Hardware RAID
Another key strength of dedicated hardware RAID controllers is more advanced drive failure protection and recovery capabilities. Hardware RAID provides excellent resilience to drive failures and data loss through features like:
- Hot spare drives – Unused spare drives can automatically rebuild failed drives for faster recovery.
- Parity RAID optimization – Specialized parity calculation abilities provide better protection and performance.
- Battery-backed cache – Cached data is saved during power loss enabling faster recovery.
- Automatic rebuild – Transparently rebuilds failed drives without admin intervention.
Software RAID usually lacks advanced rebuilding and caching abilities leading to longer exposure to data loss during drive failures. Software RAID is also dependent on the operating system – if the OS crashes or fails to load, the RAID volumes may be inaccessible even if the drives are intact.
Hardware RAID’s device-level intelligence ensures maximum uptime and data protection in the event of inevitable drive failures. Studies show hardware RAID delivers 4-8x lower annual data loss risk compared to software RAID configurations.
Flexibility Limitations of Software RAID
While software RAID provides platform flexibility since it isn’t tied to a proprietary RAID card, it lacks flexibility when it comes to migrating and adapting RAID configurations:
- Reconfiguring software RAID often requires wiping disks and rebuilding from scratch.
- Scaling software RAID capacity by adding disks is usually challenging.
- Moving software RAID between OS installations is limited or impossible.
- Software RAID locked to a specific OS, virtual platform, or server technology.
Hardware RAID configurations are portable, adaptable, and designed for easy reconfiguration:
- Adding capacity or changing RAID levels is seamless with hot-swappable drives.
- RAID volumes persist when moving cards between systems or upgrading motherboards.
- RAID cards work across operating systems and server platforms.
- Can migrate RAID volumes to new hardware RAID systems and configurations.
Hardware RAID’s implementation flexibility eases future expansions and infrastructure changes. Software RAID often locks you into a specific OS or platform restrictively.
Advanced Feature Set of Hardware RAID
Hardware RAID controllers provide an extensive set of advanced features you can’t get with software RAID solutions:
- Tiered caching – Combinations of faster SSD cache and larger memory caches to optimize read/write speeds.
- Automatic SSD caching -Machine learning algorithms place frequently accessed data on SSDs.
- Storage pooling – Aggregate different types of drives into a single volume.
- Data migration – Non-disruptive volume data movements between arrays or RAID types.
- Snapshots – Freezevolume contents in a point-in-time snapshot for backup/recovery.
Software RAID capabilities are relatively basic – providing only simple mirroring and striping options. Hardware RAID delivers enterprise-class availability, flexibility and optimizations not possible on software RAID solutions.
Hardware RAID Use Cases
Hardware RAID delivers advantages over software RAID in several key storage use cases:
Transactional Database Servers
The specialized caching and disk optimizations of hardware RAID delivers superior performance for the demanding I/O of databases like Microsoft SQL Server, Oracle, MySQL, etc. Hardware RAID provides up to 30% lower average read/write latencies for busy databases.
Business Critical Applications
For business critical apps requiring maximum uptime, hardware RAID’s advanced redundancy and automatic failover capabilities ensure availability and continuity during drive failures. Hardware RAID keeps mission critical apps online.
Virtualized Servers and SANs
Hardware RAID maximizes virtual machine density, reduces hypervisor CPU overhead, and enables more demanding workloads. Virtual SANs also heavily benefit from hardware RAID’s performance and availability features.
Media Streaming and Editing
For high resolution media streaming and editing, hardware RAID delivers the throughput and low latency needed for smooth playback and rendering. Video production workflows see big speed improvements with hardware RAID.
Cloud Storage Servers
Large cloud storage server banks running OpenStack, Ceph, and other platforms are powered by hardware RAID for scale-out performance and redundancy. The world’s largest cloud providers use hardware RAID extensively.
Conclusion
While software RAID provides a low cost way to achieve basic data redundancy, hardware RAID is superior for delivering performance, reliability, and flexibility. For any application where uptime and speed are critical factors, dedicated hardware RAID solutions are recommended over software RAID. The hardware optimized architecture of RAID cards provides significant advantages for transactional databases, virtualized infrastructure, business critical systems, and high capacity storage.