RAID (Redundant Array of Independent Disks) technology was first conceptualized in the late 1980s as a way to combine multiple disk drive components into a logical unit for the purposes of data redundancy and performance improvement (https://www.techtarget.com/searchstorage/definition/RAID). The term “RAID” was coined in 1987 by David Patterson, Randy Katz, and Garth A. Gibson in their seminal paper that outlined the fundamental RAID concepts and levels (https://medium.com/@tedyyusuf97/history-of-raid-ae458a981384).
RAID combines multiple physical disk drives into one logical drive to provide increased storage capacity, reliability, and/or performance compared to single drives. The specific benefits depend on the RAID level, but common advantages include data redundancy, improved read/write speeds, and greater storage capacity.
The key purposes of RAID are to protect against disk failures and improve I/O performance. By replicating data across multiple disks, RAID safeguards against potential data loss if a single disk fails. Spreading data access across multiple disks can also enhance disk read/write speeds for faster data throughput.
Common RAID Configurations
There are several standard RAID configurations that are commonly used for various purposes:
RAID 0 – Striping
RAID 0 stripes data across multiple drives without parity or mirroring (Source: https://en.wikipedia.org/wiki/Standard_RAID_levels). This provides improved performance compared to a single drive, but does not provide fault tolerance. If one drive fails, all data will be lost. RAID 0 is used when performance is critical and data redundancy is less important.
RAID 1 – Mirroring
RAID 1 duplicates (mirrors) data across two or more drives (Source: https://www.trentonsystems.com/blog/raid-levels-0-1-5-6-10-raid-types). This provides fault tolerance in case one drive fails, as data is duplicated on the remaining drives. Write performance may be slower compared to RAID 0 due to the duplication. RAID 1 is used when data redundancy is critical.
RAID 5 – Distributed Parity
RAID 5 stripes data across multiple drives with distributed parity information (Source: https://www.pcmag.com/news/raid-levels-explained). The parity allows data to be recovered if one drive fails. RAID 5 provides a balance of performance, capacity efficiency, and fault tolerance. It is a popular choice for server storage.
RAID 6 – Double Distributed Parity
RAID 6 is similar to RAID 5, but uses double distributed parity (Source: https://en.wikipedia.org/wiki/Standard_RAID_levels). This allows data to be recovered even if two drives fail. RAID 6 is used when fault tolerance is critical and some capacity efficiency can be sacrificed.
Advantages of RAID
One of the main advantages of RAID is improved performance compared to single drives. By spreading data across multiple disks, RAID can increase read and write speeds through parallelization. For example, RAID 0 stripes data across all disks in the array, allowing for concurrent disk accesses and faster data transfers (Techtarget, 2023).
RAID also provides fault tolerance and redundancy through parity and mirroring. RAID levels 1, 5, 6 and 10 all incorporate data redundancy so that if a drive fails, data can still be accessed and recovered from the remaining disks. This protects against data loss due to drive failures (Diskinternals, 2023).
In addition, many RAID levels allow for hot-swapping – replacing failed disks without turning off the RAID system. This facilitates recovery from drive failures and minimal downtime (Xinnor, 2023). Overall, RAID’s redundancy features offer much better protection compared to single disk drives.
Disadvantages of RAID
While RAID offers important benefits like increased performance and redundancy, it also comes with some downsides:
Added complexity – Implementing RAID requires additional hardware and software, which adds to the complexity of the storage system. This can make it more difficult to configure and manage compared to single disks (https://www.liquidweb.com/kb/raid-level-1-5-6-10/).
Potential performance bottleneck – The RAID controller can become a bottleneck that limits performance, especially for write-intensive applications. The controller has to process all reads and writes for the entire array (https://ulink-da.com/pros-and-cons-of-redundant-array-of-independent-disks-raid/).
Cost of redundancy – Storing data redundantly on multiple disks increases the cost per gigabyte of storage. RAID requires purchasing more drives than a single disk solution.
RAID in the Era of Virtualization
Virtualization has become increasingly popular in data centers and server environments over the past decade. As organizations shift towards virtualized infrastructure, the relevance of traditional RAID configurations has come into question.
With virtualization, multiple virtual servers can be hosted on a single physical server. This reduces hardware requirements and increases efficiency, but also impacts storage design. In a virtual environment, a RAID configuration applied to a physical disk is only visible to the hypervisor, not the individual virtual machines (VMs). The hypervisor handles mapping the RAID volumes to VMs.
This shift towards virtualization and software-defined storage has led to a decreased reliance on hardware-based RAID configurations. Software RAID implemented at the hypervisor level provides more flexibility than proprietary hardware RAID controllers 1. Software RAID isn’t tied to a particular physical server and can be managed independently of the hardware.
Hardware RAID controllers still have some advantages, including potentially better performance for write-intensive applications. However, for many use cases, software RAID provides equivalent redundancy and availability 2. The flexibility and cost savings of software RAID make it an increasingly popular choice in virtualized environments.
RAID Alternatives
While RAID remains popular, especially in enterprise environments, several alternatives have emerged that aim to improve upon RAID in various ways. Three of the most notable RAID alternatives are JBOD, Storage Spaces, and ZFS.
JBOD (Just a Bunch of Disks) is one of the simplest RAID alternatives. As the name suggests, JBOD simply combines multiple physical disks into a single logical volume, with no striping, mirroring, or parity. The benefit of JBOD is it maximizes storage capacity, but it lacks redundancy. JBOD is best suited for large files that do not need protection against drive failures (Source).
Storage Spaces, included in Windows 8 and newer, lets you group disks together in a storage pool. You can then create virtual disks called storage spaces from the pool. Storage Spaces supports options like mirroring, striping, and parity, similar to RAID. However, the key advantage is it allows combining drives of different sizes into a single virtual disk more flexibly than RAID (Source).
ZFS (Zettabyte File System) is an advanced file system that provides volume management as well as data integrity features like RAID. ZFS is known for scalability, supports very large storage sizes, and provides robust data protection. However, ZFS is complex to set up initially compared to traditional RAID (Source).
Use Cases Where RAID Still Makes Sense
Despite the increasing availability of alternatives, there are still some use cases where RAID remains an optimal solution:
Database Servers
RAID is commonly used for database servers that require high I/O performance and availability. RAID 10 provides the redundancy, speed, and parallelism needed for database workloads involving frequent small writes (Source). The striping improves performance while the mirroring provides fault tolerance.
High Availability Systems
For systems that need to minimize downtime, like critical business applications, RAID 1+0 can provide constant uptime and rapid recovery. The RAID 1 mirroring provides redundancy while the RAID 0 striping enables parallel I/O (Source). This makes RAID 1+0 well-suited for high availability scenarios.
Video Editing
RAID 0 is commonly used in video editing workstations to provide the bandwidth required for multiple streams of uncompressed video. The massive throughput enabled by striping across multiple drives makes RAID 0 ideal for handling high-resolution video (Source).
Declining Relevance of RAID
In recent years, the relevance of RAID for general purpose storage has declined for several reasons:
First, the availability of affordable, high-capacity hard drives has reduced the need for the efficiency and capacity gains provided by RAID. With 8TB+ consumer hard drives now commonplace, a single drive can store huge amounts of data at a low cost.
Second, cloud storage services like Dropbox, Google Drive and Amazon S3 provide highly redundant and resilient storage that essentially acts like a massive software-defined RAID array. Storing data in the cloud reduces the need for local RAID configurations.
Finally, new software-defined storage technologies like ZFS and Ceph provide RAID-like functionality without the need for specialized hardware RAID controllers. They offer more flexibility and control through software.
According to a discussion on Reddit, while hardware RAID still has a place for specific use cases, it is becoming “less and less relevant for home users” due to affordable large drives and cloud storage [1]. Another forum also concluded that RAID is declining in relevance as alternatives emerge [2].
The Future of RAID
With the rise of new storage technologies like flash storage and cloud storage, some have speculated that RAID may become less relevant in the future. However, new RAID standards are still being developed to keep pace with emerging trends. For example, the Non-Volatile Memory Express (NVMe) standard allows SSDs to connect directly to the PCIe bus, enabling much faster data transfer speeds. To take advantage of this, the NVMe RAID standard was created to support RAID implementations specifically for NVMe SSDs (https://en.itpedia.nl/2017/06/27/de-toekomst-van-raid/).
RAID will also likely become more integrated with virtualization technology. Since many servers now utilize virtual machines (VMs) rather than dedicating a whole server to one application, there is a need for RAID solutions that can operate seamlessly across the virtual environment. This may lead to “virtualization-aware” RAID implementations that can dynamically allocate resources as VMs are spun up or shut down (https://forum.huawei.com/enterprise/en/what-can-be-some-future-trends-in-raid-technology-discussion/thread/689850049326104576-667213859733254144).
New use cases for RAID may also emerge, especially as data storage needs continue to grow exponentially. For example, RAID could be applied in edge computing scenarios where data needs to be processed locally before being sent to the cloud. The redundancy of RAID provides an advantage in edge deployments that may have unreliable connectivity. RAID also remains relevant for organizations that need fast local access to huge datasets that would be impractical to store completely in the cloud. So while RAID may be declining in relevance for some applications, innovation and adaptation will likely ensure it still serves a purpose for specific use cases in the future.
Conclusion
In summary, while RAID configurations still offer benefits like redundancy and improved performance in some use cases, the technology is declining in relevance for many IT environments.
RAID retains validity for mission-critical systems that demand high availability or applications that require faster disk I/O. However, virtualized infrastructure and software-defined storage have supplanted RAID’s importance in many server rooms and data centers.
As storage technologies continue evolving, RAID’s prevalence is fading. But in select use cases, mostly involving physical servers with rigorous uptime or throughput requirements, RAID remains a sensible solution. Though its importance is waning in the broader IT landscape.