In our RAID series so far, we’ve explored in depth what RAID is, and defined it as a Redundant Array of Independent Disks or a series of hard drives linked together to store data in a specific manner. Additionally, we’ve covered different RAID levels, their meanings, uses, and advantages & disadvantages. Now that we have all this information, there’s just one question that needs to be answered: how does it all work? The answer is a RAID controller, which is a device or program that tells the computer how to handle the data it’s given and where to store it. A RAID controller is the literal brain of a RAID array, and can take the form of a hardware RAID controller or a software RAID controller. In this article we take a look at hardware RAID vs software RAID controllers, and when to use which option.
What Is Hardware RAID?
A hardware RAID solution is a dedicated processing system that contains its own processor and memory for running your RAID array. In this implementation, all hard drive disks are connected to a RAID controller which will physically control and support your RAID configuration. The role of the hardware RAID controller is to manage your hard drive disks and present them to your host computer as one or more logical units. With hardware RAID, your controllers can either be card-based as a discrete, physical card or they can be a ROC which stands for “RAID-on-Chip” technology which is integrated hardware that comes with its own motherboard. In some cases, a hardware RAID controller will be set up as an independent small computer system dedicated to your RAID application, offloading all tasks from the host computer.
Discrete Hardware RAID Controller Card
This RAID controller implementation is an expansion type card that has a built-in RAID processor sometimes called an I/O processor. It also contains its own interfaces for your hard disk drives (I/O controllers). It most commonly plugs into your motherboard’s PCIe or PCI-X slots and all RAID functionality that comes from it is completely separate from your host computer. It works by fully offloading all tasks into a redundant storage subsystem so that your host system’s performance is not impacted, even during drive failures.
Advantages of a discrete physical hardware RAID card:
- Has multiple I/O interfaces on the physical card. This allows you to expand the array by adding on as many hard disk drives as you need to boost capacity.
- Host system isn’t impacted. Having multiple RAID arrays will not impact the host system performance. You can migrate singular or multiple RAID arrays as needed to other operating systems or host systems without impact.
- RAID applications are independent of the host system. When the system crashes, the data integrity stays intact.
- Protects against power loss. Will keep track of in-progress writes, keeping data secure in the event of power loss.
- Virus protected. Hardware RAID arrays are independent from the host system, making it not vulnerable to viruses.
- Provides great performance. Hardware RAID offloads all RAID tasks from the host, giving better host system performance.
- Comes with a dedicated graphical user interface & software. Make it very easy to set up your RAID array and maintain it.
- Can migrate & replace as needed. Your physical card can be plugged into any system, replaced, or upgraded as needed.
- Supports advanced RAID features. Such as array-level migration, online expansion, and disk hot plugs.
- Comes with on-controller caching. Access times are increased as memory is cached.
Disadvantages of a discrete physical hardware RAID card:
- Expensive. It comes with a much higher cost than other RAID solutions as the end-user must purchase I/O processors and additional memory drives to expand. Beyond this, you must also purchase the physical card.
Raid-on-Chip (RoC) Hardware RAID Technology
This implementation comes as a chip that is integrated into your motherboard and usually contains the RAID processor, memory controller, host interface, I/O interfaces for your hard disk drive connections, and memory all in one.
Advantages of hardware Raid-on-Chip Technology:
- Protected at boot/startup. Array protects data during, and from the boot process, nullifying any errors.
- RAID is independent from the host computer. This protects data from system crashes.
- Not affected by viruses. The array is independent from the host system, making it not vulnerable to viruses.
- Low system impact. Offloads tasks from the host computer, making this setup suitable for RAID 5 and 6.
- On-Controller Caching. Access times are increased as memory is cached.
- Supports advanced RAID features. Such as array-level migration, online expansion, and disk hot plugs.
- Comes with a dedicated graphical user interface & software. Make it very easy to set up your RAID array and maintain it.
Disadvantages of hardware Raid-on-Chip Technology:
- Medium cost. Using less physical components than a standard physical controller reduces cost, but still costs more than software RAID.
- Low flexibility. Migration to other systems is impossible without a similar RoC solution.
What Is Software RAID?
When a RAID array is hooked up to a computer with no physical controller, the computer needs instructions on how to operate and use it. This is done with a program called a software RAID controller, which makes use of the computer’s CPU to direct information. You can implement software RAID as a pure software application that runs on your operating system, or you can use a hardware-assisted software RAID solution.
Pure Software RAID application
This solution utilizes an application that runs on the host without hardware. It uses hard disk drives that are attached directly to the computer system via a built-in I/O interface or processor-less host bus adapter. When the software is loaded up, the RAID becomes active. It is often built directly into the operating system, coming at no additional cost to the end-user.
Advantages of using a pure software RAID application:
- Comes Built Into the Operating System. There is no extra cost to have software RAID functionality when using operating system software RAID implementations.
- Highly Flexible. Especially when used in large servers, pure software RAID can be tailored to fit a variety of situations.
Disadvantages of using a pure software RAID application:
- Does not protect data against boot failure. Any corrupted data present during the boot process, before the RAID program starts, the computer will not recognize and result in it becoming inoperable.
- Additional load on system. The more resources the array needs, the more it will impact your system’s performance. A more complex RAID 5 setup will be more taxing than a RAID 0, 1, or 2 array.
- Vulnerable to viruses. Operating within the OS means viruses can impact the performance of the array in addition to the system.
- Data integrity affected by system crashes. Any hardware or software issues experienced by the system will likely affect the data in the array.
- Limited OS Migration. If you ever need to change systems or update your OS, you will be unable to if the new OS doesn’t support RAID functionality.
- No write-back cache. Where hardware RAID can run in “write-back” mode with the use of a battery, there is no way to add a battery to software RAID. This means you lose out on an extra layer of protection.
Hardware-Assisted Software RAID
This solution is a hybrid model that uses software and additional hardware to overcome pure operating system software RAID weaknesses such as no on boot protection. It works by using a RAID BIOS that is integrated into the motherboard, which protects your host system’s boot, so that any data corruption does not lead to an inoperable system. It often comes with numerous drivers for multiple operating systems, increasing compatibility.
Advantages of using hardware-assisted software RAID:
- Has a moderate cost to implement. You only need a plug-in card or an additional flash memory to implement hardware-assisted software RAID. If running a RAID 5 configuration, there is an additional expense of a hardware accelerator.
- Data is protected if the boot drive fails. If your boot drive encounters errors or fails completely, there will be no negative impact on the availability of your data.
- Easy to set up. The RAID array is easy to maintain and set up if you are using a dedicated graphical user interface with operating system software to run your RAID array.
Disadvantages of using hardware-assisted software RAID:
- Additional load on system. The more resources the array needs, the more it will impact your system’s performance. This implementation works well for RAID 0, 1, and 10 configurations.
- Vulnerable to viruses. Runs directly on the host system, so if the system becomes infected, the RAID can too.
- System crashes can harm data integrity. Data integrity and consistency are impacted by system crashes.
- Comes with limited migration. With this RAID implementation, the controller is dependent on the operating system and associated drivers. You can’t migrate without having the right drivers. For instance, if you upgrade your operating system, you may need a newer driver for your RAID array controller to work.
- No write-back cache. It only has a write-through mode, no write-back mode. Without a write-back mode, you lose a lot of write performance. You cannot add a battery onto hardware-assisted software, so you can’t get this layer of protection.
Comparing the Differences Between Hardware RAID vs Software RAID
Now that we’ve gone through the benefits and drawbacks of both implementations of hardware RAID vs software RAID, let’s take a look at how these two stack up against one another with regards to performance, compatibility, affordability, and flexibility.
| Hardware RAID | Software RAID | |
| Performance | Performs well/on-par with software RAID for basic RAID Levels. Outperforms software RAID on all complex RAID configurations. Can rebuild mirrored data at a much faster rate. If using flash storage arrays, you may have inconsistent performance with some RAID setups. | Performs well for basic RAID Levels. Performance is heavily impacted with complex RAID levels, making it unsuitable. |
| RAID Level Configurations | Has hardware enclosures that come with built-in support for all basic RAID levels. Can support all complex RAID levels but it requires additional hardware enclosures & more hard drive disks. | Basic RAID levels are supported. If you want RAID 3 or RAID 5, you need additional software. |
| Operating System Compatibility | More RAID configurations to choose from including hybrid options. Windows and MAC compatible. | Specific to the operating system being used. Cannot be shared between operating systems. Certain operating systems only support certain RAID levels. |
| Affordability | More costly to set up. | Very low cost to entry. |
| Flexibility | All hard drive disks can work as one single disk in accordance with the host operating system. Each hard drive disk enclosure/array can be moved between operating systems or computers. | Offers more flexibility with regards to how each drive can be configured in their enclosures. |
And with that said, here is what you can expect from the different RAID implementations based on their respective controllers.
| Features | Hardware RAID | Software RAID | Hardware-Assisted Software RAID |
| Boot Data Protection? | Yes. | No. | Yes. |
| Write-back Caching? | Yes. | No. | No. |
| Power Loss Protection? | Yes. | No. | No. |
| Independent of Host Operating System? | Yes. | No. | No. |
| Vulnerable to Viruses? | No. | Yes. | Yes. |
| Setup During Boot? | Yes. | No. | Yes. |
| OS Migration? | Yes. | No. | Limited. |
What Are Typical Use Cases of Hardware RAID vs Software RAID?
Now that we understand what the key differences are between hardware RAID vs software RAID, let’s dive into some typical server scenarios in which you would see these RAID controllers in action.
Hardware RAID Solutions
These types of solutions offer the most features and provide the best performance. Real-world scenarios include:
- High performance servers or workstations that require large data storage.
- Enterprise servers that require performance, scalability, flexibility, and are compatible with multiple operating systems.
Pure Software RAID Solutions
These types of solutions work really well for RAID arrays that need to excel in performance and data availability (think RAID 0 and RAID 1 configurations). It is important to note that with pure software RAID solutions, it cannot be used directly on the boot drive as it needs the operating system active to work. Real-world scenarios include:
- Workstations or servers that do not have large data storage requirements.
- Servers that do not need boot protection.
Hybrid Solutions
These are similar to pure software RAID solutions but are cost-sensitive and have boot-ability requirements. Real-world scenarios include:
- Basic servers that do not have a large data storage requirement.
- In situations where there is networked storage being used.
Which one should you choose, hardware or software RAID?
In general, hardware RAID is going to provide you with a lot more advantages over software RAID, especially if you are looking to implement a complex RAID configuration or a hybrid model. The main consideration is the price you are willing to pay for your RAID controller.
RAID Level comparisons
Now that you are able to pick the ideal RAID controller for your system, it’s time to choose the right RAID level to use. We have created several in-depth comparisons to make the decision easier:
