Solid state drives (SSDs) are becoming increasingly popular for use in servers, workstations, and personal computers. SSDs offer much faster read/write speeds compared to traditional hard disk drives (HDDs). This makes them desirable for applications that require high performance storage. However, SSDs have lower storage capacities than HDDs. To increase capacity, redundancy, and performance, SSDs can be configured into RAID (Redundant Array of Independent Disks) arrays.
Quick Answers
Yes, SSDs can be configured into RAID arrays. The benefits of using RAID with SSDs include:
- Increased overall storage capacity
- Improved performance through parallelization
- Added data redundancy and fault tolerance
The most common RAID levels used with SSDs are RAID 0, RAID 1, RAID 5, and RAID 10. Each offers different tradeoffs between capacity, performance, and fault tolerance. RAID can be implemented via hardware RAID controllers or in software.
What is RAID?
RAID (Redundant Array of Independent Disks) is a data storage technology that combines multiple disk drives into a logical unit. Data is distributed across the drives in one of several ways called RAID levels, depending on the required level of redundancy and performance. The main purposes of RAID are to:
- Increase capacity – Multiple disk drives are combined into a single logical unit, creating a much larger storage space.
- Improve performance – Data is distributed across multiple drives that can be read and written to in parallel, increasing speed.
- Add redundancy – Additional parity data is stored, allowing data reconstruction if a drive fails.
RAID arrays can be created with different physical hard disk drives or solid state drives. The specific RAID level determines how data is organized and redundancy is achieved. Some key RAID terms include:
- RAID 0 – Also called disk striping. Data is split across drives for faster reads/writes, but there is no redundancy.
- RAID 1 – Also called disk mirroring. Data is duplicated on a second drive for redundancy.
- RAID 5 – Data is striped across drives with distributed parity allowing single drive failure tolerance.
- RAID 10 – Combines mirroring and striping for both performance and redundancy.
Benefits of Using RAID with SSDs
There are several benefits to using RAID with solid state drives (SSDs):
Increased Overall Capacity
SSDs currently have much lower capacities compared to hard disk drives. Consumer SSDs commonly range from 120GB to 4TB. Enterprise models may reach 16TB. By combining multiple SSDs in a RAID 0 configuration, the overall array capacity is equal to the sum of the individual drives. For example, four 2TB SSDs would create a 8TB RAID 0 array.
Faster Read and Write Speeds
SSDs are capable of very fast read and write speeds, far above traditional hard drives, due to their lack of moving parts and NAND flash memory technology. RAID 0 and other striped RAID levels read and write data in parallel across multiple SSDs, which multiplies their effective speeds. Four SATA SSDs in RAID 0 can achieve over 1000MB/s transfer rates.
Increased Fault Tolerance
Like all storage media, SSDs can still fail unexpectedly. Certain RAID levels like 1, 5, and 10 provide data redundancy, allowing the array to continue operating if a drive fails. The failed drive can also be replaced and data rebuilt from the remaining SSDs. This provides greater data reliability for important applications.
Improved IOPS
SSDs provide excellent random input/output operations per second (IOPS) performance which is important for transactional workloads like databases. By combining SSDs into arrays, their high IOPS capabilities are multiplied. For example, a database server with 800K IOPS needs might use a 5 SSD RAID 10 array to achieve 4 million IOPS.
Disadvantages of Using RAID with SSDs
While SSD RAID arrays provide significant benefits, there are also some tradeoffs to consider:
Increased Cost
The main disadvantage of an SSD RAID setup is increased cost. SSDs are still pricier per gigabyte than HDDs. Populating a RAID array with multiple SSDs will be expensive. However, the performance and reliability gains often justify the cost for critical applications.
Complexity
Configuring, managing, and troubleshooting a RAID array requires additional expertise compared to standalone drives. IT staff managing the array need RAID-specific knowledge. There is also added complexity in picking the right RAID level to match technical and business requirements.
Write Performance Impact
RAID levels with parity such as RAID 5 and 6 incur a write performance penalty. The parity data needs to be calculated and written with each write operation, which adds overhead. Therefore, write speeds will be lower than RAID 0 or 1. Reads are unaffected.
Decreased Usable Capacity
Mirrored RAID levels like RAID 1 and 10 effectively halve the usable capacity, as data is duplicated. RAID 5 and 6 also reduce usable capacity due to the space needed for parity data. The reduction varies based on array size and RAID level.
RAID Levels Used with SSDs
There are several standard RAID levels that are commonly deployed with SSDs:
RAID 0
- Also called disk striping
- Data is split and distributed evenly across all drives in the array
- Provides maximum capacity and parallel performance
- No redundancy – any drive failure results in total data loss
- Best suited for speed-critical needs where redundancy is less important
RAID 1
- Also known as disk mirroring
- Data is fully duplicated on a second drive
- Provides good read performance and redundancy with two drives
- 50% usable capacity due to mirroring
- Simplest redundant RAID level suitable for many use cases
RAID 5
- Data striped across drives with distributed parity stripes
- Can withstand the failure of one drive without data loss
- Slower write speeds due to parity calculation
- Usable capacity is (N-1) drives worth due to parity overhead
- Good option for cost-efficient redundancy
RAID 10
- Combines mirroring and striping
- Provides speed, capacity, and redundancy
- Requires a minimum of 4 drives
- 50% usable capacity
- High cost but excellent performance and fault tolerance
Implementing RAID with SSDs
SSD-based RAID arrays can be implemented in several ways:
Hardware RAID
A hardware RAID controller manages the array. It provides a dedicated storage processor, cache memory, and sometimes battery backup. Hardware RAID advantages include:
- Does not consume host system resources
- Dedicated RAID processor offloads RAID calculations
- Provides caching to boost performance
- Simple to configure through controller BIOS
Hardware RAID disadvantages:
- More expensive due to controller hardware costs
- Less flexibility – locked into controller vendor feature sets
Software RAID
RAID is implemented in software without specialized hardware. The operating system or third-party software handles RAID calculations. Software RAID advantages include:
- Much lower cost – uses existing system resources
- Vendor neutral – mix and match drives from any brand
- More flexible configuration options
Software RAID disadvantages:
- Consumes CPU resources for RAID processing
- Lacks dedicated data caching
- Configuration can be more complex
Overall, hardware RAID is simpler to use but more expensive. Software RAID offers more customization and lower cost.
Operating System RAID
Modern operating systems like Windows, Linux, FreeBSD, etc. have built-in software RAID capabilities. This allows creating RAID arrays without any additional hardware or software. OS-based RAID provides a low cost option that is suitable for smaller arrays and less critical workloads. The limited feature set may not meet the needs of larger or more demanding applications.
Caching RAID Controllers
A hybrid approach is to use an inexpensive RAID controller that provides caching capabilities. This helps boost array performance compared to pure software RAID. Battery backup on the cache is recommended to prevent data loss on power failure. Overall, caching RAID controllers offer a good middle-ground option.
Ideal RAID Configurations for SSDs
Based on their technical characteristics and strengths, certain RAID levels tend to work better for SSD arrays:
RAID 0 for Performance
If read/write performance is the top priority, RAID 0 is ideal. The massive parallel bandwidth of SSDs in a striped set offers incredible speed. Just ensure to have backups – RAID 0 provides no redundancy.
RAID 10 for Balance
For critical data that requires both speed and redundancy, RAID 10 is often the best fit for SSDs. Its combination of mirroring and striping offers the performance of RAID 0 and the fault tolerance of RAID 1.
RAID 5 for Budget Redundancy
If the cost of RAID 10 is prohibitive, RAID 5 can provide more affordable redundancy by distributing parity stripes across drives. Write speed is slower than RAID 0/10 but most reads will be fast.
RAID 1 for Simplicity
RAID 1 is the easiest mirroring option that doesn’t require calculating and writing parity. It can provide adequate redundancy and read speed for non-critical applications on a budget.
SSD RAID Use Cases
Here are some examples of where SSD RAID arrays are commonly used for performance gains and redundancy:
- Web & Database Servers – Use RAID 10 to provide fast random IOPS performance for heavy transactional workloads while also minimizing downtime from any SSD failures.
- High Performance Compute – For supercomputing clusters or AI/ML training, large RAID 0 arrays exploit SSD parallelism and speed to feed data to GPUs as fast as possible.
- Media & Entertainment – RAID 0 stripes high-bitrate video across SSDs to support smooth editing, effects, and rendering for 4K/8K content.
- Virtualized Servers – Hyperconverged infrastructure with VMware or other platforms can leverage SSD RAID storage to deliver fast performance for virtual machines.
- Desktop Workstations – For professional media creation, software development, etc., internal SSD RAID gives creators reliability and awesome speeds when working with huge files.
Comparison of SSD RAID vs HDD RAID
SSD and HDD RAID arrays have quite different strengths and weaknesses:
| SSD RAID | HDD RAID | |
|---|---|---|
| Read Speed | Much faster, 1000+ MB/s with RAID 0 | Capped around 200 MB/s max even with RAID 0 |
| Write Speed | Much faster, 900+ MB/s with RAID 0 | Capped around 150 MB/s max with RAID 0 |
| Latency | Extremely low latency in microseconds | Higher latency in milliseconds due to physical seeks |
| Availability | 99.9% or better is achievable | 99.9% or better is achievable |
| IOPS | High IOPS in the hundreds of thousands | Much lower IOPS, usually below 10,000 |
| Capacity | Lower capacities, maxing out around 64 TB currently | Much higher capacities available, up to 1 PB on some arrays |
| Cost | More expensive per GB | Lower cost per GB |
Should You Use RAID with SSDs?
The dramatic speed, performance, and reliability improvements of SSD RAID arrays make them highly beneficial for the following use cases:
- Transactional databases
- Real-time analytics
- Virtualized servers
- High performance computing
- Video editing & production
- Critical applications requiring maximum uptime
For general office file serving, backup, and archival storage where capacity is the top concern and performance requirements are light, HDD RAID remains a more budget-friendly option. However, with SSD prices declining yearly, all-flash arrays are becoming viable even for secondary storage uses.
Conclusion
RAID and SSDs are clearly very compatible technologies. Combining them unlocks substantial performance and redundancy benefits. With incredible throughput exceeding 1 GB/s and high IOPS to handle heavy workloads, SSD RAID delivers blazing speed that HDD RAID cannot match. Options like RAID 10 provide fast transactional capability while also minimizing downtime. For applications that demand the utmost in storage performance or reliability, SSD RAID arrays are now the premier choice.
