RAID (Redundant Array of Independent Disks) is a data storage technology that combines multiple disk drive components into a logical unit. RAID systems distribute data across multiple drives to provide increased data reliability and/or increased input/output performance. RAID was first conceptualized in the late 1980s by David Patterson, Garth Gibson and Randy Katz at the University of California, Berkeley[1].
The key goals of RAID are to provide fault tolerance and improve performance. Fault tolerance means if one disk fails, the data can still be accessed from the remaining disks. Improved performance comes from spreading data across multiple disks which can be accessed in parallel. There are different RAID levels or architectures that provide different tradeoffs between things like speed, capacity and redundancy.
The most common RAID levels are:
- RAID 0 – Data is striped across disks for performance, but provides no redundancy.
- RAID 1 – Disk mirroring for redundancy, but no performance gain.
- RAID 5 – Data is striped across disks with distributed parity for redundancy.
- RAID 6 – Similar to RAID 5 but with double distributed parity.
Choosing the right RAID level involves balancing performance, capacity, redundancy and cost for a particular application. Higher RAID levels generally provide more redundancy at the expense of available capacity.
RAID 0
RAID 0, also known as disk striping, is a RAID configuration that splits data evenly across two or more drives without parity information. The benefit of RAID 0 is enhanced disk performance at the cost of fault tolerance (https://recoverit.wondershare.com/windows-tips/what-is-raid-0.html).
With RAID 0, data is broken down into blocks and each block is written to a separate disk drive. This allows for simultaneous read/write operations across multiple disks, offering faster performance. The more disks added, the greater the performance boost (https://www.pitsdatarecovery.com/raid-0-array/).
However, RAID 0 provides no data redundancy or fault tolerance. If one drive fails, all data across the array will be lost. For this reason, RAID 0 is best suited for non-critical data where performance is paramount and data backups exist.
RAID 1
RAID 1, also known as disk mirroring, involves copying data identically to multiple drives (at least two). This provides redundancy in case one drive fails. With RAID 1, data is written to all drives simultaneously, so read performance can be faster since the reads can be distributed across different drives. However, RAID 1 does not provide increased write speeds.[1] The number of drives used in a RAID 1 array does not affect read or write performance. At a minimum, RAID 1 requires two hard drives and provides redundancy through mirroring.
RAID 1 is well suited for situations requiring high redundancy to protect data, but does not offer performance gains from striping data across multiple disks. The disadvantage is that 50% of total storage capacity is used for redundancy, which can be inefficient for large arrays.[2]
RAID 5
RAID 5 utilizes striping with distributed parity. This means that data is striped across multiple drives like in RAID 0, but parity information is also distributed across the drives (Understanding RAID Performance at Various Levels). The parity allows for fault tolerance, as if one drive fails, the data can be recreated from the remaining data and parity information. RAID 5 requires at least 3 drives to implement.
A major benefit of RAID 5 is good redundancy – the array can withstand the failure of one drive. The distributed parity also offers decent performance, as writes do not have to wait for a dedicated parity drive. Reads can approach speed of a striped RAID 0 array. However, write speeds are slower than RAID 0 since parity information must be updated each write (RAID5 Speed Question).
In general, more drives in a RAID 5 array can provide faster speeds, though performance does degrade during rebuilds after a disk failure. The more disks, the longer the rebuild takes. RAID 5 offers a good balance of redundancy and performance for arrays with 3+ drives.
RAID 6
RAID 6 utilizes striping with double distributed parity. This means that data is striped across multiple drives like with RAID 0, but it also stripes parity information across the drives as well. Parity allows for fault tolerance by allowing data on a failed drive to be recreated from the remaining data and parity information. By using double distributed parity, RAID 6 can withstand the failure of up to two drives without losing data (Petri, 2022).
The main advantage of RAID 6 over RAID 5 is the added redundancy. RAID 5 can only handle a single drive failure before data loss occurs. RAID 6 allows two drive failures, providing additional protection against hardware failures. However, this added redundancy comes at a cost – RAID 6 has slower write speeds than RAID 5 since it has to calculate and write more parity data. RAID 6 also requires a minimum of 4 drives, whereas RAID 5 can be created with as few as 3 drives (TechTarget, 2021).
While RAID 6 has slower speeds than RAID 5, increasing the number of drives can help improve performance. More drives allow the write operations to be distributed, decreasing the performance hit from the parity calculations. So for setups with a larger number of disks, RAID 6 can provide faster speeds than RAID 5 while still providing the superior redundancy (Reddit, 2022).
References:
Petri. (2022). RAID 5 vs RAID 6: How to Choose the Best RAID Configuration. https://petri.com/raid-5-vs-raid-6/
TechTarget. (2021). RAID 5 vs. RAID 6: Capacity, performance, durability. https://www.techtarget.com/searchdatabackup/tip/RAID-5-vs-RAID-6-Capacity-performance-durability
Reddit. (2022). If raid 5 is no longer recommend nor is raid 6, what do I do? https://www.reddit.com/r/DataHoarder/comments/10ve6dz/if_raid_5_is_no_longer_recommend_nor_is_raid_6/
RAID 10
RAID 10 utilizes both data striping and disk mirroring for increased performance and redundancy.[1] In RAID 10, data is striped across multiple drives like in RAID 0, providing fast read and write speeds. At the same time, the striped data is mirrored like in RAID 1, providing fault tolerance in case a drive fails.[2]
With RAID 10, data is written in stripes across multiple drives simultaneously, enabling fast write performance that scales linearly with the number of drives.[3] For example, four drives in RAID 10 can deliver close to 4x the write performance of a single drive. The more drives added, the faster the overall performance becomes. However, there is a tradeoff that RAID 10 requires an even number of drives, with half used for striping and half for mirroring. So there is 50% storage efficiency due to the mirroring.
RAID 10 provides fast speeds and redundancy, making it a popular choice for applications requiring both high performance and fault tolerance. The combination of striping and mirroring makes RAID 10 well-suited for environments with more demanding storage needs and larger numbers of drives.
[1] https://www.ibm.com/docs/en/i/7.4?topic=concepts-how-raid-10-affects-performance
[2] https://blog.serverfault.com/2010/07/11/798854017/
[3] https://www.arcserve.com/blog/understanding-raid-performance-various-levels
RAID 50
RAID 50 is a combination of RAID 5 and RAID 0, combining distributed parity with striping for performance and redundancy across a large number of drives.
RAID 50 arrays use RAID 5 groups with distributed parity which provides the redundancy of RAID 5. These groups are then striped using RAID 0 to spread data over all the disks, improving performance. This makes RAID 50 well-suited for setups with a large number of drives, as more drives increases the parallelism of reads and writes. According to https://www.reddit.com/r/sysadmin/comments/13vpfg9/the_best_way_to_arrange_raid_on_24_disks_in_new/, RAID 50 is a good option for maximizing performance on 24 drives while still providing redundancy.
Since RAID 50 combines the distributed parity of RAID 5 with striping, it provides redundancy to handle drive failures but can also greatly improve performance through increased parallelism as the number of drives increases. The tradeoff is reconstruction after drive failures can be more complex than other RAID levels.
RAID 60
RAID 60 combines disk striping and parity protection from RAID 6 with the increased performance from RAID 0 (Microsemi). It stripes data across the disks similar to RAID 50, but also adds a second distributed parity block like RAID 6. This provides protection against up to two disk failures (Broadcom).
The tradeoff is slower performance compared to RAID 50, but higher redundancy. RAID 60 requires a minimum of 8 drives, but performance increases with more drives since the distributed parity allows for more parallel access (Spiceworks Community). The ideal use cases are large storage arrays where performance is still important but high redundancy is critical.
Recommendations
When choosing the best RAID level based on the number of drives, it’s important to consider the tradeoffs between performance, capacity, and redundancy. Here are some guidelines:
For 2 drives:
– RAID 0 provides the highest performance but no redundancy. Use when performance is critical and data loss is acceptable.
– RAID 1 provides redundancy through mirroring but cuts storage capacity in half. Use when redundancy is critical.
For 3-4 drives:
– RAID 5 provides a good balance of performance, capacity, and redundancy for a small number of drives. Data is striped and parity is distributed across drives.
For 5-8 drives:
– RAID 6 provides better redundancy than RAID 5 but write performance suffers. Use when redundancy is critical.
For 8+ drives:
– RAID 10 combines mirroring and striping for enhanced performance and redundancy. Capacity is halved compared to the number of drives.
– RAID 60 offers the redundancy of RAID 6 with the performance of RAID 0 but requires a minimum of 8 drives.
In general, lean towards RAID 10 for performance-critical applications and RAID 6 for redundancy-critical applications. Evaluate your specific needs for capacity, performance, and uptime when selecting a RAID level.
Conclusion
When selecting the best RAID configuration for a given number of drives, the primary considerations are redundancy, performance, and cost. RAID 0 provides the best performance but no redundancy. RAID 1 provides redundancy through mirroring but sacrifices storage capacity. RAID 5 provides a good balance of performance, redundancy, and storage capacity. As the number of drives increases, RAID 6 becomes preferable for the dual parity protection. RAID 10 provides excellent performance and redundancy but at a higher cost. RAID 50 and 60 scale the benefits of RAID 5 and 6 to larger drive counts. The optimal choice depends on your use case, data protection needs, and budget.
The most important factors are determining the level of redundancy required, if performance or storage capacity is of higher priority, and the total number of drives. Evaluate your specific requirements, weigh the pros and cons, and select the RAID that best aligns with your goals.