RAID, which stands for Redundant Array of Independent Disks, is a data storage technology that combines multiple disk drive components into a logical unit. RAID allows data to be distributed across multiple drives, providing increased storage capacity, performance, and redundancy for failure protection. But what does RAID mean specifically when applied to solid state drives (SSDs)?
Basic Concept of RAID
The basic concept behind RAID is that data is split up and stored across multiple disk drives. This is known as “striping” the data. A RAID setup requires a RAID controller to manage how the data is distributed across the disks. There are different RAID “levels” that determine how many disks are used and how the data is handled:
- RAID 0: Also called disk striping. Data is split across multiple disks for faster performance but there is no redundancy.
- RAID 1: Disk mirroring. Data is copied to a duplicate set of disks for redundancy.
- RAID 5: Disk striping with distributed parity. Data and parity information is striped across multiple disks. The parity allows for data recovery if a disk fails.
- RAID 6: Similar to RAID 5 but with double distributed parity information for higher fault tolerance.
- RAID 10: Combination of disk mirroring (RAID 1) and disk striping (RAID 0) for both redundancy and performance.
The key goals of RAID are to provide increased storage capacities, faster data access and throughput, and protection against disk failures. As long as one disk survives, data can still be recovered in most RAID setups.
Benefits of RAID for SSDs
The benefits that RAID provides for traditional hard disk drives (HDDs) also apply to solid state drives (SSDs). However, SSDs have particular characteristics that can make RAID especially useful.
Increased Performance
SSDs are much faster than HDDs, so creating a RAID array of multiple SSDs can provide considerable performance improvements. The parallelization of reads and writes across multiple SSDs means significantly faster access to data. High bandwidth RAID levels like RAID 0, 5, and 10 are well suited to leverage the speed of SSDs. Performance gains are multiplied with each SSD added to the array.
Added Storage Capacity
While SSD costs continue to decline, HDDs still provide more storage capacity per dollar spent. Creating a RAID array of multiple SSDs allows you to increase the total capacity. Depending on the RAID level, total storage can be the combined capacities of each SSD. So four 250 GB SSDs in RAID 0 would provide 1 terabyte (TB) of storage.
High Availability and Redundancy
Like with HDDs, RAID can provide redundancy with SSDs in case of disk failure. RAID levels 1, 5, 6, and 10 offer protection that if one SSD fails, data can still be recovered from the remaining disks. This is crucial for high availability and preventing data loss in mission critical systems or enterprise environments. The redundancy gives you time to replace failed drives without disrupting operations.
RAID Performance with SSDs
One of the biggest advantages of using RAID with SSDs is the performance benefits. Let’s compare some common RAID levels and how they impact SSD performance:
RAID 0
RAID 0 (disk striping) spreads data evenly across multiple SSDs with no redundancy. This level provides the best performance since read/write operations can be done in parallel. Measured speeds on a RAID 0 SSD array can potentially equal the sum of each SSD’s individual speeds. For example, two 500 MB/s SSDs in RAID 0 could achieve 1000 MB/s transfer speeds. The trade-off is increased risk of data loss if any drive fails.
RAID 1
RAID 1 (disk mirroring) provides redundancy by duplicating all data across a pair of SSDs. This protects against disk failure since data is always copied between the drives. Read performance can be boosted since reads can be distributed across both SSDs. However, write performance does not improve much since every write must go to both mirrored drives. Overall RAID 1 SSD performance is similar to a single SSD.
RAID 5
RAID 5 stripes data and parity information across multiple SSDs (minimum of 3). The distributed parity allows for data recovery if an SSD fails. RAID 5 performs well for reads since they can be split across drives, but write performance suffers due to parity calculation overhead. Most RAID 5 setups see a 50-75% write performance reduction versus RAID 0. Overall performance is better than a single SSD, but slower than RAID 0.
RAID 10
RAID 10 combines disk mirroring (RAID 1) and disk striping (RAID 0). Data is mirrored across pairs of SSDs, and those mirrored pairs are then striped. This provides both redundancy and fast performance. Writes are slower than RAID 0 since data has to be written to both disks in the mirror. But reads can be parallelized across all drives. Overall, RAID 10 delivers read performance close to RAID 0 with the redundancy of RAID 1.
Ideal RAID Configurations for SSDs
When deciding which RAID level to use for an SSD array, you’ll need to balance performance needs with your budget and required level of redundancy. Here are some ideal RAID setups for SSDs in different scenarios:
Minimum Redundancy
If redundancy is not a major concern, and maximum performance is the priority, then RAID 0 is the best option. Use at least four SSDs to get good performance gains. In RAID 0, the more SSDs, the faster the array. Just be aware of increased risk of data loss with no parity or mirroring.
Balanced Performance and Redundancy
For a balance of speed and redundancy, RAID 10 is a great choice. Four SSDs is a good starting point, arranged into two mirrored pairs that are then striped (RAID 1+0). RAID 10 provides performance close to RAID 0 but with the ability to survive a single SSD failure. Adding more mirrored pairs further improves redundancy.
Maximum Redundancy
If redundancy and data protection are critical, such as in mission-critical databases or enterprise environments, consider either RAID 5 or RAID 6. RAID 5 requires a minimum of three SSDs, while RAID 6 needs at least four. Both provide good read speeds along with single or dual drive failure protection. The dual parity of RAID 6 offers the highest level of redundancy.
Cost-effective Redundancy
If budget is a concern but redundancy is still important, start with RAID 1 using two SSDs. While you won’t get performance gains, a RAID 1 mirror protects against disk failure at the lowest cost. You can then add additional mirrored pairs of SSDs over time.
RAID Management for SSDs
A hardware or software RAID controller is required to manage RAID configurations on SSDs. Here are some options:
Hardware RAID Controller
A dedicated hardware RAID controller manages the RAID array. These plug into PCIe slots on the motherboard and handle all RAID optimization and processing. Hardware controllers provide the best performance but cost more. Popular options include cards from LSI, Adaptec, and HP.
Motherboard RAID Support
Many motherboards have built-in support for RAID, usually RAID 0, 1, 5, and 10. This integrated RAID uses system resources but can be convenient and cost-effective. Performance depends on the quality of the implementation.
Software RAID
RAID can also be managed in software without any special hardware. Linux and Windows have software RAID options built into the operating system. The configuration and management is handled by the OS, which uses the system’s CPU. Performance may not be as good as dedicated RAID hardware.
RAID on SSD Enclosures
External enclosures that house multiple SSDs will often include built-in RAID capabilities. This allows creating a portable high-speed RAID array. Popular options include enclosures from OWC, Sabrent, and TerraMaster that support RAID 0, 1, 5, and 10.
TRIM and SSD RAID
An important consideration with SSD RAID arrays is support for the TRIM command. TRIM helps maintain the performance and lifespan of SSDs by clearing invalid data blocks that are no longer in use. However, many RAID controllers do not support passing TRIM commands to the SSDs. Without TRIM, performance will degrade over time as unused cells get cluttered with old data.
Make sure your RAID controller properly supports TRIM/UNMAP if using SSDs. Hardware RAID cards that handle TRIM include ones from LSI, Adaptec, Areca, and HighPoint. For software RAID, Windows and Linux support TRIM with SSDs. Finally, some SSDs have their own garbage collection to compensate if TRIM is not enabled, but this is not as efficient as TRIM.
RAID Bottlenecks with SSDs
To maximize the advantage of RAID with SSDs, other system components need to be robust enough to fully utilize the SSD array’s speed. Potential bottlenecks include:
- CPU – An older or low-core-count CPU can limit RAID performance. Use a modern processor with at least 4 cores.
- RAM – System memory provides caching for SSD reads/writes. Faster and higher capacity RAM improves RAID performance. Aim for at least 16GB DDR4 DRAM.
- Motherboard – Must have enough PCIe lanes for maximum throughput on NVMe SSDs in a RAID array. X399 or X599 chipsets recommended for best results.
- Cabling – Use SAS cables for SATA SSD RAID arrays, or PCIe 4.0 or higher NVMe cables for NVMe SSD RAID.
- RAID Controller – Hardware RAID cards need enough cache and fast processors to manage SSD RAID efficiently.
Conclusion
The benefits of RAID become amplified when using fast solid state drives. Combining multiple SSDs into a RAID array can provide huge performance and capacity improvements. Striped RAID levels like 0, 5, and 10 are best suited for leveraging SSD speeds, while RAID 1 and 5 offer redundancy. With the proper supporting hardware, SSD RAID delivers best-in-class storage performance and reliability for mission critical applications and high demand workloads.