RAID 5 can be implemented in either hardware or software. The key difference is where the RAID calculations and parity information are processed and stored. With hardware RAID 5, this is handled by a RAID controller card or chips on the motherboard. Software RAID 5 relies on the operating system and drivers to control the RAID 5 array.
What is RAID 5?
RAID 5 is a storage technology used to protect against data loss due to drive failures. It requires at least three drives and uses distributed parity along with block-level striping. This means data is written across multiple drives in a RAID 5 array, with parity information also distributed across the drives. If one drive fails, the parity blocks allow the data on the failed drive to be recalculated from the remaining drives.
Key characteristics of RAID 5:
- Requires at least 3 drives
- Data is striped across drives at the block level
- Parity is distributed across all drives
- Can withstand one drive failure without data loss
- Read performance is good due to load balancing across drives
- Write performance reduces compared to a single drive due to parity calculations
Hardware RAID 5
With hardware RAID 5, the RAID logic and operations are handled by a dedicated RAID controller. This can be in the form of an add-on PCIe RAID card with its own onboard cache memory. Many motherboards also have RAID controller chips built-in that allow you to configure RAID arrays through the BIOS.
The key advantage of hardware RAID 5 is that it offloads the CPU-intensive parity calculations required for RAID 5 from the host computer’s CPU. This means the impact on overall system performance is lower compared to software RAID 5 implementations. Hardware RAID 5 also frees up host resources like CPU and RAM that would otherwise be consumed by software RAID operations.
Advantages of hardware RAID 5:
- Lower CPU usage since RAID calculations handled by controller
- Frees up host resources like CPU and memory
- Onboard cache improves write performance
- Hardware accelerators can offload RAID parity computations
- Dedicated controller guarantees consistent performance
Disadvantages of hardware RAID 5:
- Higher cost due to add-on RAID cards or enabled motherboards
- Limited flexibility compared to software RAID
- Dependent on RAID controller and proprietary drivers
- Rebuilding array relies on RAID controller cache
Software RAID 5
With software RAID 5, the RAID management is handled by the operating system and drivers. The CPU performs the parity calculations needed for the RAID 5 array. Most modern operating systems like Windows, Linux and macOS include software RAID capabilities.
Software RAID 5 provides more flexibility since it does not depend on any specific RAID hardware. Arrays can be created from inexpensive drives connected via SATA, SAS or USB. But the downside is the performance overhead on the host system due to the CPU-intensive parity computations.
Advantages of software RAID 5:
- Low cost solution using inexpensive drives
- OS and driver dependent rather than hardware
- More flexibility in array creation and management
- Can utilize drives from different interfaces like SATA, SAS, USB
Disadvantages of software RAID 5:
- CPU usage is higher due to parity calculations
- Potential impact on overall system performance
- Dependent on OS and driver support
- No onboard cache so lower write performance
When to choose hardware vs. software RAID 5?
There are some general guidelines on when to choose hardware or software RAID 5:
- Hardware RAID 5 for mission critical environments where performance is paramount
- Hardware RAID 5 for transactional workloads with heavy writes to minimize overhead
- Software RAID 5 for cost-sensitive environments using commodity drives
- Software RAID 5 for systems where hardware RAID support is limited
- Software RAID 5 for setups where flexibility in array management is needed
Hardware RAID 5 tends to be used in enterprise and server environments where the investment in a high-end RAID controller is justified by performance demands. Software RAID 5 is more commonly used in desktops, home servers and other cost-focused setups where flexibility is prioritized over raw performance.
Can you combine hardware and software RAID 5?
It is possible to combine both hardware and software RAID 5, which offers some of the advantages of both implementations. This hybrid RAID 5 setup requires RAID controller hardware combined with RAID management through the operating system.
For example, a hardware RAID card can be used to provide the performance benefits of its onboard cache and parity computation acceleration. But the RAID arrays are created and managed through software RAID utilities rather than the RAID BIOS.
The benefit of this hybrid RAID 5 approach is the ability to take advantage of hardware optimizations while maintaining the flexibility of software RAID management. The downside is added complexity in configuring and maintaining the solution.
Benefits of hybrid hardware + software RAID 5:
- Hardware acceleration minimizes performance overhead
- OS/software RAID provides flexibility in management
- Can leverage features of both hardware and software
- Scalable and cost-effective solution
Drawbacks of hybrid hardware + software RAID 5:
- Added complexity in setup and maintenance
- Potential driver and compatibility issues
- Increased risk of misconfiguration causing errors
- Troubleshooting issues more difficult with hardware+software
Performance Differences
One of the key differences between hardware and software RAID 5 is in performance:
| Performance Metric | Hardware RAID 5 | Software RAID 5 |
|---|---|---|
| Read speed | Fast | Slower due to CPU overhead |
| Write speed | Faster with onboard cache | Slower due to parity calculations on CPU |
| Latency | Lower latency | Higher latency |
| CPU usage | Minimal impact on CPU | Higher CPU utilization |
| Flexibility | Limited flexibility | Very flexible |
As seen in the table, hardware RAID 5 generally outperforms software RAID 5 in terms of throughput, latency and CPU usage. But software RAID 5 provides much more flexibility. So there is a classic tradeoff between raw performance and flexibility.
Real-world performance impact:
In real-world tests, hardware RAID 5 can deliver 2-3x higher throughput compared to software RAID 5, particularly for write-heavy workloads. For light workloads and sequential reads, the difference is narrower. But hardware RAID consistently has lower latency and CPU overhead.
For transactional apps with sustained reads and writes, hardware RAID 5 is the clear winner. The performance gap closes for more archival type workloads dominated by large sequential reads. But even there, hardware RAID usually wins out due to advantages in multi-queue depth performance.
Reliability Differences
Both hardware and software RAID 5 provide protection against a single drive failure. After that, their reliability differs based on implementation factors:
- Controller cache – Hardware RAID 5 uses capacitor-backed or NVDIMM caches that help complete ongoing writes if power is lost. Software RAID 5 lacks this protection.
- Rebuilds – Hardware RAID rebuilds tend to be faster due to optimized controllers and onboard caches. Software rebuilds impact overall system performance.
- Hot spares – Hardware RAID makes hot spares easier to implement. They take over instantly in case of a failed drive.
- Alerting – Hardware RAID controllers have dedicated health monitoring and alerts. Software relies on OS notifications.
- Drives – Enterprise hardware RAID uses specialized drives rated for 24/7 operation. Software RAID uses off-the-shelf drives.
Due to these factors, business-critical deployments tend to favor hardware RAID 5 for the additional reliability capabilities it offers. But software RAID 5 can match reliability if enterprise-class drives are used and the system is adequately provisioned.
Management Differences
Managing RAID 5 arrays also differs significantly between the hardware and software approaches:
- Interfaces – Hardware RAID is managed via vendor BIOS/firmware tools. Software RAID uses OS utilities or external apps.
- Ease of use – Hardware RAID management tends to be simpler and less varied between vendors. Software RAID varies based on OS environment.
- Features – Hardware RAID supports more mature feature sets around caching, tiering, snapshots etc. Software RAID has fewer optimization capabilities.
- Automation – Hardware RAID automation uses vendor management tools plus extensions. Software RAID relies more on OS and third-party scripting capabilities.
- Virtualization – Software RAID integrates more tightly with hypervisors for virtualized management capabilities.
Software RAID provides more flexibility, while hardware RAID is generally simpler to manage at scale. For large deployments, hardware RAID management capabilities tend to be more robust and tightly integrated.
Cost Differences
Hardware RAID 5 requires a significant upfront investment in RAID controllers compared to software RAID 5 running on commodity hardware:
- Hardware RAID controller – $400 to $3000 depending on features
- Software RAID uses existing hardware
But hardware RAID can lead to lower operating expenses long-term thanks to simplified management and higher efficiency. The higher capital costs are justified for mission critical storage. Software RAID is extremely cost effective for secondary storage uses not requiring the highest performance.
Scenarios where hardware RAID 5 has lower TCO:
- Transactional databases with heavy read/write loads
- High performance compute clusters
- Business critical applications with SLAs
- High throughput streaming workloads
Scenarios where software RAID 5 has lower TCO:
- Bulk storage for backups, archives etc.
- ReadOnly media libraries and repositories
- Lightly used infrastructure with modest I/O needs
Conclusion
RAID 5 can be implemented via dedicated hardware RAID controllers or via software through the operating system. Hardware RAID 5 maximizes performance and simplifies management, at the cost of less flexibility and higher upfront pricing. Software RAID 5 provides outstanding cost-efficiency and flexibility, but falls short of hardware RAID in raw throughput and latency.
For mission critical systems that require high resiliency, hardware RAID 5 is often the right choice despite higher acquisition costs. It minimizes performance overhead while providing robust management tools. For less demanding storage needs where cost is king, software RAID 5 exploits the processing power of x86 CPUs at little incremental expense.
The choice between hardware and software RAID 5 involves a careful evaluation of performance, reliability, operational and cost considerations. There is no universally superior option, as the optimal approach depends entirely on the specific business needs and IT environment. Hybrid RAID 5 setups attempt to deliver the best of both worlds, but add complexity. By understanding the core strengths and limitations of each approach, IT organizations can implement the RAID 5 solution that provides the ideal balance for their application workloads and infrastructure strategies.
