Are RAID drives SSD?

This is a common question for those exploring data storage options. RAID (Redundant Array of Independent Disks) is a data storage technology that combines multiple disk drives to act as a single storage unit. SSD (solid-state drive) is a type of high-performance storage that uses flash memory rather than spinning platters. So are RAID drives considered SSD? Let’s explore this in more detail.

Table of Contents

What is RAID?

RAID is a technology that combines multiple physical disk drives and makes them act as a single logical drive. Data is distributed across the drives in the array. This provides improved performance, redundancy, and/or larger storage capacities compared to single drives. Some key advantages of RAID include:

Increased read/write performance – spreading data across multiple disks allows for simultaneous access.

Redundancy – RAID levels like 1, 5, 6, 10 provide fault tolerance if a drive fails.
Larger storage pools – multiple disks added together provide more total storage capacity.

There are different RAID “levels” that determine how data is distributed across the array. Some common ones include:

RAID 0 – Data is striped across disks for faster performance, but there is no redundancy.
RAID 1 – Disks are mirrored for redundancy. If one fails, the other contains a complete copy of the data.
RAID 5 – Data is striped across disks with parity information for redundancy distributed across the array.

RAID 10 – Combination of mirroring and striping for both performance and redundancy.

The main benefits of RAID are increased speed, capacity, and fault tolerance compared to single disk systems. RAID requires specialized RAID controllers to manage the array and calculate parity for data redundancy.

What are SSDs?

SSDs, or solid-state drives, are a type of high-speed storage device that uses integrated circuit assemblies and flash memory to store data persistently. Unlike hard disk drives (HDDs), SSDs contain no moving mechanical components. Key advantages of SSDs include:

Faster read/write speeds – SSDs can access data much more quickly than HDDs.
Better durability – More shock and vibration resistant with no moving parts.
Lower latency – Very low access times for individual data requests.

Compact – Smaller form factors available compared to HDDs.

Because of their incredible speed and performance, SSDs are increasingly becoming the preferred storage option for things like operating systems, programs, and primary data storage. Their higher cost per gigabyte is dropping steadily as manufacturing scales up. However, HDDs still maintain cost advantages for very large secondary storage needs.

Differences Between RAID and SSD

While both RAID and SSD can improve storage performance, they actually do it in very different ways:

RAID combines multiple disk drives to act as one. This allows for distribution of data across drives for speed and redundancy.
SSD uses non-volatile flash memory chips to store data on integrated circuits rather than magnetic platters. This allows for much faster access speeds.

RAID is a logical layer that abstracts multiple physical disks into a single virtual drive. SSD is a specific type of hardware storage device that uses flash memory and has no moving parts.

RAID can be set up using either HDDs or SSDs as its underlying physical storage media. For example, you could create a RAID 10 array using four SSD drives. This would give you both the redundancy of RAID 10 along with the speed advantages of SSDs.

RAID drives themselves are not SSD. As explained above, RAID is a technique for combining multiple physical drives into a single logical unit. SSD is a type of drive hardware that uses non-volatile flash memory rather than spinning platters.

However, RAID can be implemented using either HDDs or SSDs as its underlying storage media. For example:

A RAID 1 array using two HDD drives is not an SSD RAID.
A RAID 5 array using three SSD drives is an SSD RAID.

So in summary:

RAID refers to the logical array, not the physical media.
SSD refers specifically to the solid-state flash memory media.
RAID using HDDs is not SSD.

RAID using SSDs is SSD RAID.

Advantages of SSD RAID

Combining SSDs into a RAID array can provide tremendous performance benefits compared to HDD RAID or single SSD drives. Some key advantages include:

Faster reads/writes – spreading I/O across multiple SSDs increases total bandwidth and throughput.

Redundancy – RAID levels like 1, 5, and 10 provide fault tolerance against drive failure.
Performance scaling – adding more SSDs linearly increases total array performance.
Flexibility – can customize RAID level based on performance vs. redundancy needs.

SSD RAID can achieve incredible speeds far exceeding single HDDs or SSDs. For example, a RAID 0 array of four PCIe SSDs can reach speeds over 10,000 MB/s with very low access latency. This makes it ideal for applications like video editing, databases, virtualization, and gaming.

The downside is cost – SSD RAID has a higher price point than HDD RAID or single SSDs. However, as SSD costs continue to decrease, SSD RAID is becoming more affordable for a wider range of applications.

SSD RAID Use Cases

Some examples where high performance SSD RAID makes sense despite the cost premium:

Database servers – Need fast transaction processing and high IOPS.
Web/caching servers – Very high read and write throughput required.
High-end workstations – Video editing, 3D rendering, data science.

Virtualized environments – Reducing latency and IO bottlenecks.

Disadvantages of SSD RAID

While SSD RAID offers speed and flexibility, there are some downsides to consider as well:

Increased cost – SSD RAID has a higher upfront investment compared to HDD RAID.

Complexity – Requires RAID controller and may need tweaking for optimal performance.
Potential waste – Unused SSD capacity does not add redundancy unlike HDD RAID.

You also need to select the most appropriate RAID level for your use case. Levels like RAID 0 offer pure speed but no fault tolerance. RAID 5 provides redundancy but write speeds may suffer due to parity calculation overhead.

RAID Controller Considerations

To build an SSD RAID array, you will need a compatible RAID controller. This is a hardware device that manages the RAID logic, IO to the drives, and any caching. Key factors to consider include:

Interface – PCIe NVMe controllers offer the fastest SSD connectivity and maximum throughput.
RAID level support – Entry-level cards may only support RAID 0/1 where higher-end cards can do 5, 6, 10, 50/60.

Cache memory – More cache improves read performance and write buffering.
Additional features – Some controllers have battery backups, SSD overprovisioning, or self-encryption.

Advanced hardware RAID cards like those from Broadcom or Intel offer the best performance but can get quite expensive. Many motherboards these days also have basic onboard RAID capabilities via chipsets like AMD RAID-X or Intel RST.

Software vs. Hardware RAID

For SSD RAID, you also have a choice between hardware or software RAID implementations:

Hardware RAID – Uses dedicated RAID card and processor for RAID calculations and disk IO.
Software RAID – RAID logic is handled by OS and system CPU instead of specialized hardware.

Hardware RAID offers better performance since it offloads processing overhead from the CPU. But software RAID can still provide very good performance with modern multicore CPUs, and avoids the cost of a RAID card.

For most common desktop and general business use, software RAID is probably sufficient. But for mission critical environments like databases or high performance computing, hardware RAID is preferable, or even a must.

Software RAID Options

Some popular software RAID options include:

Windows – Storage Spaces, Disk Management utility
Linux – mdadm, LVM
Storage Spaces (Windows) – Allows creating storage pools and virtual drives with flexible RAID options. Great for managing multiple disks.

mdadm (Linux) – Powerful CLI-driven utility for managing advanced software RAID configurations in Linux.

RAID Performance Considerations

When architecting an SSD RAID array, performance tuning and optimization is critical to extract maximum throughput from the drives. Here are some key considerations:

RAID Configurations

RAID 0 – Ideal for peak read/write throughput but no redundancy.

RAID 10 – Provides excellent random I/O performance while still having fault tolerance.
RAID 5 – Good read speed and redundancy but write performance may suffer due to parity overhead.

Stripe Size

The stripe size determines how data is distributed across the drives. Larger stripes mean more sequential throughput but can reduce random I/O performance in some cases. Typical stripe sizes are 64KB, 128KB, 256KB, or larger depending on workload.

SSD Alignment

Proper partition alignment avoids unnecessary read-modify-write inefficiencies. Alignment should be checked against stripe size and SSD page size.

Queue Depths

Higher queue depths allow more parallel IO requests but require sufficient RAM capacity. Queue depths around 32-128 are typical for high performance SSD RAID.

Overprovisioning

Adding extra unallocated space on the SSDs improves performance and endurance. 20% overprovisioning is typical but some workloads may benefit from more.

Comparison of Storage Options

Let’s compare some of the main single drive vs. RAID options available if you need fast storage performance:

Storage Type	Read Speed	Write Speed	IOPS	Redundancy
Single HDD	100 MB/s	100 MB/s	100-200	No
Single SSD	500 MB/s	300 MB/s	10,000-100,000	No
HDD RAID 0	600 MB/s	600 MB/s	400-1000	No
SSD RAID 0	2,500 MB/s	1,500 MB/s	100,000-500,000	No
HDD RAID 10	400 MB/s	300 MB/s	400-1000	Yes
SSD RAID 10	2,000 MB/s	1,000 MB/s	80,000-400,000	Yes

As you can see, SSD RAID 10 provides an excellent balance of high speed, redundancy, and great random I/O performance making it ideal for applications like databases and critical data storage.

Conclusion

In summary:

RAID is a logical abstraction and does not refer to a specific physical storage media like SSDs.
SSDs provide faster access speeds than HDDs but at a higher cost per gigabyte.
Combining SSDs into a RAID configuration provides the speed of SSDs along with the redundancy and logical management of RAID.

SSD RAID offers tremendous performance benefits compared to single HDDs or SSDs in key areas like databases, virtualization, video editing and more.
Proper RAID controller selection and configuration tuning is key to maximizing the performance and reliability of an SSD RAID array.

While SSD RAID has a higher upfront cost, it offers unmatched storage performance when optimized properly. As SSD costs continue to fall, high speed SSD RAID will become accessible to more applications and use cases where top-tier storage IO is critical.