RAID (Redundant Array of Independent Disks) is a data storage technology that uses multiple drives to provide increased performance, capacity, and reliability compared to single drives. RAID works by writing data across multiple drives in a pattern determined by the RAID level. There are many different RAID levels, each optimized for different use cases. With SSDs (Solid State Drives), RAID can provide significant performance and data protection benefits thanks to the speed of SSDs.
SSDs provide much faster read/write speeds than traditional hard disk drives (HDDs) due to their lack of moving parts and use of flash memory. However, SSDs on their own still carry a risk of data loss if a drive fails. By combining multiple SSDs in a RAID array, read/write speeds can be further improved through parallelization while also introducing redundancy to protect against drive failure. The best RAID configuration for SSDs depends on the priorities of performance, capacity, and data protection.
RAID 0
RAID 0, also known as striping, stripes data across multiple drives. This means the data is split into blocks and distributed evenly across the array of drives. The main benefit of RAID 0 on SSDs is increased performance. Since data is written simultaneously to multiple drives, read and write speeds can be significantly faster than a single SSD (Is an SSD RAID 0 worth it?).
Some benchmarks show nearly double the sequential read/write speeds on RAID 0 SSD arrays compared to a single SSD, especially with higher drive counts like 4 SSDs (SSDs in RAID 0: Still Makes Sense?). This makes RAID 0 ideal for tasks like video editing, 3D modeling, simulations and other bandwidth-intensive applications.
However, there is no data redundancy with RAID 0. If one drive fails, all data across the array will be lost. So reliability and fault tolerance are sacrificed for performance (Is RAID 0 SSD Worth It for Gaming). RAID 0 SSD arrays are best suited for temporary storage and scratch disks where data loss is not critical.
RAID 1
RAID 1, also known as disk mirroring, is a RAID configuration that uses mirrored disks for redundancy (Source). With RAID 1, data is written identically to two or more drives simultaneously. If one drive fails, the data can still be accessed from the other mirrored drive(s). This provides fault tolerance and improves read performance, since data can be read in parallel from multiple drives.
The key advantages of RAID 1 include enhanced data security and an improved data throughput rate. By duplicating data across multiple disks, RAID 1 provides protection in case of a single disk failure. The array can continue operating with one failed drive, allowing time for the failed drive to be replaced and rebuilt without downtime (Source). However, RAID 1 offers no parity or striping, so it does not provide protection against multiple simultaneous drive failures.
RAID 1 can be a good choice for SSDs when redundancy and faster reads are desirable, but it does come at the cost of reduced usable capacity. Each data copy reduces the total capacity by the size of an individual drive. Some also argue the redundancy of RAID 1 is less beneficial for SSDs, which are statistically less likely to fail than mechanical hard drives (Source).
RAID 5
RAID 5 stripes data and parity information across multiple drives (source). This level provides fault tolerance by dedicating the equivalent of one drive’s worth of space across the array to parity data. If a single drive in a RAID 5 array fails, the parity information can be used to reconstruct the lost data. While commonly used with HDDs, RAID 5 does have some downsides when used with SSDs.
Since SSDs have a limited number of write cycles, the constant parity writes in RAID 5 can shorten the lifespan of the SSDs (source). The parity drive is under constant stress as it has to be updated each time data is written. This makes it more prone to failure than the other drives. Additionally, rebuilding an array after a drive failure places significant stress on the remaining SSDs.
Overall, RAID 5 provides redundancy for SSD arrays, but at the cost of decreased write performance and longevity compared to other RAID levels. The continuous parity writes should be considered when using RAID 5 with SSDs.
RAID 10
RAID 10, also known as RAID 1+0, combines disk mirroring and disk striping to offer both data redundancy and increased performance (TechTarget). In RAID 10, data is written in stripes across multiple drives while also being duplicated on a mirror set of drives. This provides fault tolerance from drive failures as well as improved speed from the striped set.
Specifically, RAID 10 requires a minimum of 4 drives, with data written in stripes across half the drives and mirrored onto the other half. For example, with 4 drives you would have 2 stripes mirrors. If one drive fails, the mirror set ensures there is still an intact copy of the data. RAID 10 can sustain multiple drive losses so long as no more than 1 drive is lost from each mirror set. In addition, by striping data across multiple drives, RAID 10 allows for increased performance, especially for read operations.
The combination of mirroring and striping makes RAID 10 well-suited for applications that require both data redundancy and high performance, such as databases or virtualization. However, RAID 10 is inefficient in storage capacity as half the total capacity is taken up by mirroring. RAID 10 works best with high performance SSDs to take advantage of their fast data transfer speeds.
RAID Controller
When it comes to RAID setups, you have two main options for the RAID controller: dedicated hardware RAID controllers or software-based RAID handled by the operating system. Dedicated RAID controllers are specialized PCIe cards designed specifically for managing RAID arrays. They contain a fast processor, battery-backed cache, and either dedicated XOR hardware or an ASIC to handle parity calculations. This offloads the computational work from the CPU.
Software RAID relies on the CPU and operating system to handle all RAID calculations and management. The main advantage of software RAID is cost – you don’t need to purchase a dedicated hardware controller. However, it can impact performance since the CPU has to handle the RAID tasks. Software RAID also lacks features like battery-backed cache found on hardware controllers.
For SSD arrays, a dedicated hardware RAID controller generally provides better performance compared to software RAID. The hardware controller reduces latency by handling the RAID tasks, while also providing extra features optimized for SSDs. However, software RAID can be sufficient for home or small business use cases where maximum performance is not required.
TRIM Support
TRIM is an important SSD command that helps maintain performance over time. As you write and delete data on an SSD, pages get marked as invalid. Without TRIM, the drive will still read these invalid pages when scanning for free space, which slows down write performance. TRIM allows the operating system to notify the SSD which blocks of data are no longer valid, allowing the SSD controller to stop scanning those pages for free space and improve performance (https://www.techtarget.com/searchstorage/definition/TRIM).
Enabling TRIM ensures the SSD controller can efficiently perform garbage collection and keep write speeds closer to when the drive was brand new. TRIM commands are sent whenever you erase files or format a drive. Most modern operating systems have TRIM enabled by default for SSDs. Make sure it is active if you want optimal and consistent SSD performance over time.
SSD-Optimized RAID Levels
Certain RAID levels have been designed specifically to take advantage of the performance characteristics of solid-state drives (SSDs). These SSD-optimized RAID levels aim to maximize both performance and data protection for SSD storage environments.
One example is RAID 5DP (Double Parity). This is an enhanced version of standard RAID 5 that provides two parity drives instead of one. The extra parity drive protects against multiple drive failures, which is important for SSDs since they tend to fail unpredictably compared to HDDs. RAID 5DP helps prevent data loss in SSD RAID 5 arrays (1).
Another SSD-focused RAID level is RAID 10DM (Dual Mirrored). RAID 10DM combines mirroring and striping but with two mirrors per stripe instead of the standard single mirror. This increases redundancy for better data protection. The multiple mirrors also enhance performance for write-heavy workloads often seen with SSDs (2).
In general, RAID levels optimized for SSDs aim to take advantage of the ultra-fast read/write speeds of SSDs while mitigating their higher failure rates compared to HDDs. The focus is on performance as well as redundancy for data protection.
Caching
SSDs offer greatly improved read/write performance and latency compared to traditional HDDs. However, SSDs are still significantly more expensive per GB. SSD caching looks to deliver some of the performance benefits of SSDs while minimizing costs by only using a small amount of SSD storage to cache frequently accessed data.
SSD caching, sometimes referred to as tiered storage, involves using a small SSD as a high-speed cache for a larger HDD volume. The SSD cache stores copies of frequently accessed data for low latency retrieval. Subsequent reads of any data in the cache are served from the SSD rather than the HDD, improving overall performance.
SSD caching can provide a significant performance boost for workloads with a high proportion of repeated reads. The caching effectiveness depends heavily on the workload and access patterns. SSD caching is ideal for random read-intensive workloads. For large sequential workloads that exceed cache capacity, the benefits will be limited.
Enabling caching on the SSD portion of a RAID array can help reduce latency and improve IOPS. This is especially true for random, read-heavy workloads. The performance gains over a non-cached RAID array will depend on the size of the SSD cache and the access patterns.
Some key benefits of using SSD caching include:
- Faster access to frequently read data
- Improved read latency and IOPS
- Cost savings compared to an all SSD array
- Works with HDD RAID arrays to improve performance
Overall, SSD caching aims to deliver significantly improved storage performance while minimizing costs. For read-intensive workloads, it can provide performance approaching full SSD speeds. However, caching benefits are highly dependent on workloads and proper cache sizing.
Recommendations
SSDs continue to increase in popularity and capability, making them excellent candidates for use in RAID arrays. However, traditional HDD-focused RAID implementations are not always ideal for SSDs. Experts recommend optimizing your RAID configuration to maximize the performance and longevity of your SSD storage.
RAID 10 is generally considered the best RAID level for SSDs, offering a balance of speed, capacity, and redundancy. The striping maximizes read/write speeds, while the mirroring provides fault tolerance in case of drive failure. RAID 10 evenly distributes writes across drives to promote even wear. One downside is 50% storage efficiency due to mirroring. HDD or SSD – What to Choose for RAID Setup
RAID 5 and 6 can work with SSDs, but frequent writes can lead to uneven wear and impact lifespan. The parity calculations also create a minor performance bottleneck. Some experts recommend avoiding RAID 5/6 for SSD arrays if possible. RAID 0 offers maximum speed and capacity utilization, but no redundancy.
Enable TRIM support for your SSDs whenever possible. TRIM frees up unused blocks on the SSD, maintaining performance over time. Use SSD caching to boost speeds for HDD-based arrays. Monitor SSD wear levels and preemptively replace drives nearing end of life. Choose enterprise-grade SSDs designed for constant operation if budget allows.