What is a RAID Controller?
A RAID controller is a hardware device that manages hard drives in a RAID (Redundant Array of Independent Disks) configuration (PCMag, 2022). The controller connects to multiple hard drives and presents them to the computer as a single logical drive. This allows for improved performance, fault tolerance, and ease of use compared to managing each drive independently.
The controller handles the RAID configuration calculations and processes, such as striping data across drives for speed, mirroring drives for redundancy, or parity calculations for error checking. This offloads the RAID workload from the CPU and operating system. The controller also manages hot swapping of failed drives and rebuilding RAID arrays when a new drive is inserted to replace a failed one (NEC, 2022).
Overall, a dedicated RAID controller provides the intelligence behind building flexible arrays of hard drives that can be tuned for performance, capacity, or availability within a single logical volume. This simplifies storage management and provides capabilities beyond what motherboard integrated RAID can offer.
Improved Performance
RAID controllers use techniques like striping and caching to significantly improve disk performance compared to a single disk drive. Striping spreads data across multiple drives, allowing reads and writes to occur in parallel, accelerating throughput. Controllers also utilize memory caches to reduce disk access latency. Writes are first staged in RAM then later flushed to disk, while frequently accessed reads are served directly from cache. These optimizations enable RAID arrays to achieve speeds exceeding that of individual disks. According to TechTarget, hardware RAID controllers tend to offer better performance than software RAID due to having dedicated processing resources. However, high-end server CPUs can deliver competitive software RAID throughput.
Source: Key differences in software RAID vs. hardware RAID
Fault Tolerance
Fault tolerance refers to the RAID controller’s ability to withstand and recover from hard drive failures without loss of data. This is an essential feature of RAID controllers that sets them apart from basic disk controllers.
RAID levels like RAID 1, 5, 6, and 10 provide varying degrees of fault tolerance by writing data redundantly across multiple drives. For example, RAID 1 mirrors data identically across two drives. If one drive fails, the other still has a complete copy of the data. Meanwhile, RAID 5 stripes data and parity information across three or more drives, allowing the array to reconstruct the data if a single drive fails. According to AC&NC, RAID 6 offers double distributed parity and can withstand up to two drive failures.
Without fault tolerance, a single drive failure could cause complete data loss and system downtime. By providing redundancy, RAID controllers allow easy replacement of failed drives without loss of access or data. This delivers vital protection for mission-critical storage systems.
Ease of Use
One of the main benefits of using a dedicated RAID controller is that it makes setting up and managing RAID arrays much simpler compared to software RAID solutions. The RAID controller handles all of the complexity behind the scenes, allowing you to easily configure and monitor RAID arrays through a straightforward interface. This simplifies common tasks like creating arrays, adding disks, rebuilding failed disks, and migrating arrays to new systems.
RAID controller interfaces, whether hardware-based or accessed through software, provide central points to manage all connected disks and arrays. This allows administrators to avoid configuring RAID settings individually in the operating system or BIOS. Leading hardware controllers include built-in wizards to guide users through setup and optimization. Software RAID solutions can require editing configuration files manually, executing disk commands, and integrating various tools.
By offloading RAID tasks to dedicated hardware or software, system resources are freed up for other workloads. Software RAID relies on the CPU for parity calculations and other array operations, while hardware RAID shifts this burden. For large disk arrays or busy systems, this difference in overhead can be significant.
Overall, purpose-built RAID controllers greatly simplify storage tasks compared to DIY software RAID. Their interfaces streamline setup, monitoring, and maintenance, while reducing the learning curve and chances for human error.
Advanced Features
A hardware RAID controller provides additional capabilities beyond just combining drives for improved performance and fault tolerance. Some advanced features offered by RAID controllers include:
Snapshots – With snapshot capabilities, the RAID controller can create point-in-time copies of volumes that can be used for backups or testing. Snapshots only copy changed data, so they require less storage space. This allows restoring data to a previous snapshot if needed.
Cloning – RAID controllers support cloning volumes, which creates an exact copy that can be used for testing patches or upgrades, developing applications, or data analysis. The clone acts as a separate volume.
Encryption – Many RAID controllers support encrypting data on the fly to provide an extra layer of security. This protects sensitive data in the event drives are lost or stolen.
Caching – RAID controllers utilize memory caching to boost performance for read and write operations. This provides faster access to frequently used data.
Queue depth – More advanced RAID controllers offer larger queue depths to allow more I/O operations to be processed simultaneously. This improves efficiency for transactional workloads.
Remote management – IT administrators can remotely configure, monitor and manage RAID controllers from anywhere which improves efficiency.
These extra capabilities allow a RAID controller to provide more than just the core RAID levels. The advanced features enhance performance, security, data protection and administrative convenience.
Hardware vs Software RAID
Hardware RAID uses a dedicated RAID controller, which is a specialized circuit board that handles the RAID calculations and organization. Software RAID relies on the main CPU and operating system to perform these functions. There are pros and cons to each approach:
Pros of hardware RAID:
- Better performance – the RAID controller optimizes all I/O operations without taxing the CPU
- Increased reliability – the RAID controller operates independently of the OS
- Simpler to setup – most hardware RAID solutions are plug and play
Cons of hardware RAID:
- More expensive – dedicated RAID cards cost more than software solutions
- Limited flexibility – changes to the RAID setup often require configuring the RAID card’s BIOS
- Vendor lock-in – RAID cards may only work with certain motherboards/drives
Pros of software RAID:
- Cost effective – uses existing resources so no added hardware costs
- Flexibility – software RAID setups can be modified without hardware changes
- Standardized – OS-based solutions work across different hardware
Cons of software RAID:
- Performance overhead – taxes the CPU and slows down overall system
- OS dependent – requires OS support and drivers to function
- No hardware redundancy – still relies on main system components
Overall, hardware RAID provides better performance while software RAID offers more flexibility. For mission critical systems that demand maximum throughput, most experts recommend using dedicated RAID cards. For home and small office builds where cost is a bigger factor, software RAID may provide sufficient redundancy.
Choosing a RAID Controller
When selecting a RAID controller, there are several key factors to consider:
Bus type – The bus interface is how the RAID controller connects to the motherboard. Common options include PCIe, SATA, and SAS. PCIe offers the fastest throughput, while SATA and SAS provide more ports and connectivity for drives. Newer PCIe 3.0 and 4.0 controllers provide the best performance overall (RAID Controller Buying Guide).
Number of ports – Determine how many drives you need to connect, both now and for future expansion. More ports allow you to add more storage drives. High port count RAID cards support large drive arrays and provide room to grow (How to Choose a RAID Controller by Configuration).
Cache memory – Cache improves performance by storing frequently accessed data, reducing load times. More cache (often 512MB or more) enables faster data throughput. Battery-backed write caches protect data in case of power loss (How to pick a RAID controller).
RAID levels – The RAID card must support your required RAID level and features. RAID 0 offers striping for speed, while RAID 1 provides drive mirroring for redundancy. Consider your performance and protection needs (RAID Controller Buying Guide).
Leading Brands
Some of the most popular and well-known RAID controller manufacturers include:
- LSI: Now owned by Broadcom, LSI is one of the leading producers of RAID controllers for enterprise and high-end markets. They are known for performance, reliability and advanced software features. LSI RAID controllers can be found in many data centers and servers.
- Adaptec: A major maker of RAID controllers for over 30 years, Adaptec focuses on delivering reliable RAID solutions for SMBs, workstations and gaming PCs. Their cards offer a balance of performance, affordability and ease-of-use.
- Areca: This Taiwanese manufacturer specializes in advanced RAID controllers for SMBs, workstations and enthusiasts. Areca controllers are packed with cutting-edge features, SSD optimization and strong RAID data protection capabilities.
- HighPoint: Offering NVMe and SAS/SATA RAID controllers, HighPoint delivers high-performance storage connectivity for workstations, servers and desktops. Their cards provide excellent throughput for demanding applications.
There are many other excellent RAID controller brands as well, but the ones above represent some of the biggest and most well-established names in the industry.
Budget Considerations
RAID controllers can range widely in price, from around $100 for basic SATA controllers up to $1,000 or more for high-end SAS controllers meant for enterprise use. Here are some tips for balancing performance and budget when choosing a RAID controller:
For consumer or small business storage needs, a basic SATA controller in the $100-$300 range from brands like LSI or Adaptec is usually sufficient. These provide good RAID 5/6 support for SATA drives at a reasonable cost.
For premium performance with SSDs or for managing many high capacity HDDs, consider a mid-range SAS controller in the $400-$700 range. These offer 12Gbps speeds, 1GB or more cache, and RAID 5/6/10 support for SAS drives.
At the top end, 12Gbps SAS controllers with 2GB+ cache and battery backups for cache can cost over $1,000. Evaluate whether those enterprise-level features are truly needed for your use case before spending more.
Buying previous generation 6Gbps controllers can also save money. While they lack 12Gbps speeds, 6Gbps SATA III and SAS are still relevant for hard drive storage.
Consider buying a used RAID controller to save significantly over new, but be sure to get one still under warranty coverage. Dell, HP, and IBM refurbished units are good options.
Overall, identify your must-have RAID features, IOPS needs, and drive types to narrow the field. Buying more controller than truly necessary can be an expensive mistake.
When You Need a RAID Controller
A dedicated RAID controller makes sense in situations where you need increased performance, robust fault tolerance, or advanced management capabilities compared to software RAID solutions (https://www.techtarget.com/searchstorage/tip/Key-differences-in-software-RAID-vs-hardware-RAID).
Some common use cases where a hardware RAID controller shines:
- Managing a storage array with many drives (6+), where the I/O load would overwhelm the host computer’s CPU.
- Running disk intensive applications like video editing, 3D modeling, or scientific computing that require high throughput.
- Maximizing uptime for mission-critical systems through advanced RAID configurations like RAID 6 or RAID 10.
- Adding enterprise-level features like global hot spares, auto-rebuilding, storage virtualization, and dynamic RAID level migration.
- Centralizing storage management by decoupling physical disks from individual servers.
- Legacy compatibility and guaranteed driver support for older operating systems.
Overall, businesses that demand consistent performance at scale will benefit from hardware acceleration and management capabilities of a dedicated RAID controller (https://www.techtarget.com/searchstorage/definition/RAID-controller). For home users or basic file sharing, software RAID is often sufficient.