What is RAID?
RAID (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 disks, providing increased data reliability and/or increased input/output performance compared to a single disk.
The concept of RAID was first outlined in the late 1980s by researchers at the University of California, Berkeley (https://www.reddit.com/r/CrackWatch/comments/ikl73c/a_brief_history_of_raid_operations_against_the/). The goal was to achieve reliable and high-performance data storage systems using inexpensive and less reliable PC hard disk drives rather than expensive mainframe hard disk drives. Since then, RAID technology has evolved into several standardized architectures (RAID 0, 1, 5, etc) that provide different combinations of increased data reliability and input/output performance.
At the core, RAID aims to provide redundancy and/or improved performance by coordinating operations across multiple physical disks. Some key techniques used include:
- Mirroring: Storing identical copies of data on multiple disks.
- Striping: Splitting data across multiple disks to distribute workload.
- Parity: Storing calculated error-correcting information to recover lost data if a disk fails.
Benefits of RAID
RAID offers several key benefits that make it an attractive storage solution for many situations:
Increased redundancy – By spreading data across multiple disks, RAID can protect against data loss if one disk fails. For example, in a RAID 1 configuration, data is mirrored on two disks so there are two copies. If one disk fails, the data can still be accessed from the other disk.
Improved performance – RAID can allow for faster read and write speeds compared to a single disk. In RAID 0, data is striped across multiple disks, allowing for simultaneous disk access. This makes RAID 0 well-suited for applications that demand high performance.
Ability to recover from drive failures – When a disk in a RAID array fails, the failed drive can be replaced and the RAID can be rebuilt using the data on the remaining disks. This allows the RAID to return to normal operation. The ability to recover from drive failures is a key benefit of redundant RAID levels like RAID 1, 5, 6, and 10.
According to Diskinternals, RAID arrays provide far greater storage capacity compared to single disks. The redundancy of RAID offers protection against data loss from drive failure. Specific RAID levels also provide performance benefits ideal for different use cases.
Disadvantages of RAID
One disadvantage of RAID is the increased cost compared to single drives. Implementing RAID requires purchasing additional drives, a RAID controller, and in some cases extra hardware. This increased hardware investment can make RAID systems expensive to set up. However, the benefits of redundancy and performance often outweigh the higher initial costs for many organizations (Advantages and Disadvantages of Raid Levels).
A second disadvantage is complexity. Configuring and managing a RAID system requires more technical expertise compared to single drives. If the RAID configuration is not set up properly, it can negatively impact performance or result in data loss. Maintaining and monitoring RAID involves additional administrative overhead (Pros and Cons of Redundant Array of Independent Disks (RAID)).
Finally, rebuild times can be a disadvantage of some RAID levels. When a drive fails in RAID 5 or RAID 6, rebuilding the array requires reading data from all remaining drives. This rebuild process can take hours or days with large RAID arrays, during which time the system is vulnerable to a second drive failure resulting in data loss (RAID Level 0, 1, 5, 6, 10: Advantages, Disadvantages, and Use Cases).
RAID 0
RAID 0, also known as disk striping, is a RAID configuration that splits data evenly across two or more hard disk drives without parity information (redundancy). The main benefit of RAID 0 is enhanced disk performance (https://www.techtarget.com/searchstorage/definition/RAID-0-disk-striping).
Because RAID 0 distributes data across multiple disks, input/output (I/O) operations can be performed in parallel, improving throughput. Disk striping enhances performance by allowing multiple disk drives to read and write data at the same time.
However, RAID 0 provides no data redundancy or fault tolerance. If one drive fails, all data will be lost. For this reason, RAID 0 is generally used in environments where performance is more important than data redundancy (https://www.pcmag.com/encyclopedia/term/raid-0).
RAID 1
RAID 1 is a data storage configuration that utilizes disk mirroring to provide redundancy and increase fault tolerance (What is disk mirroring (RAID 1)? A definition from …). With RAID 1, data is written identically to two separate drives simultaneously. This means if one drive fails, the data can still be accessed from the mirror drive without any loss (Definition of RAID 1).
The main benefit of RAID 1 is full redundancy – if one drive fails, there is an exact copy of the data on the mirror drive. This protects against data loss in the event of a drive failure. The trade-off is that RAID 1 requires double the storage capacity for full redundancy since the data is copied to two drives. RAID 1 also provides improved read performance, since data can be read in parallel from both drives (RAID Levels Explained).
Overall, RAID 1 is best suited for situations where fault tolerance and avoiding downtime from drive failure is more important than storage capacity. The mirrored data provides full redundancy at the cost of using double the storage space.
RAID 5
RAID 5 is a RAID configuration that uses distributed parity and striping to provide redundancy and improve performance. It requires a minimum of 3 drives. In RAID 5, data is striped across all drives in the array, similar to RAID 0. However, parity information is also calculated and written across the drives. The parity information allows for data recovery in the event of a single drive failure.
RAID 5 stripes data and parity information across all drives. If one drive fails, the parity information can be used to reconstruct the data from the failed drive. This provides fault tolerance without requiring mirroring of drives like in RAID 1. RAID 5 provides good performance, capacity efficiency, and redundancy for arrays with many large drives. The distributed parity helps distribute the write load across multiple drives for better performance compared to RAID 1 or RAID 10.
However, RAID 5 does come with some drawbacks. Rebuilding an array after a drive failure can take a long time due to the need to recalculate parity information. The array is also vulnerable during the rebuild process. RAID 5 write performance can suffer due to the parity calculation. Also, the likelihood of a second drive failure increases in larger arrays, leading to potential data loss.
RAID 10
RAID 10, also known as RAID 1+0, combines disk striping and disk mirroring to provide increased performance and fault tolerance compared to other RAID levels (TechTarget, 2022). In RAID 10, data is striped across multiple disks like in RAID 0, but it is also mirrored like in RAID 1 (Acronis, 2018). This means the data is duplicated onto another set of disks.
Specifically, RAID 10 requires at least 4 disks. The data is first mirrored onto 2 disks, and then the mirrored data sets are striped across multiple sets of mirrored disks. This provides the performance benefits of RAID 0 striping, while also providing the fault tolerance of RAID 1 mirroring (TechTarget, 2022). If one disk fails, the mirrored disk can continue servicing requests without performance degradation or data loss.
The main benefits of RAID 10 include increased I/O performance and full redundancy. The drawback is that it requires at least 4 disks, so it is more costly than RAID 1 or RAID 0 alone. Overall, RAID 10 provides a balance of performance, capacity, and fault tolerance for mission critical applications that require high uptime and I/O throughput (Acronis, 2018).
Mixing Drive Sizes in RAID
Most RAID controllers allow you to mix drives of different sizes in a RAID array. However, there are some potential downsides to doing this:
When rebuilding the array after a failed drive, the rebuild time will be determined by the size of the largest drive. So if you mix a 2TB drive with two 1TB drives in a 3-drive RAID 5 array, rebuilding the 2TB drive will take longer than if all drives were 1TB. This exposes the array to greater risk of a second drive failure during rebuild. [1]
Unequally sized drives also lead to wasted space. Using the example above, up to 1TB of the 2TB drive will go unused, since the total capacity is limited by the smaller 1TB drives. So there is inefficient use of storage. [2]
In general, it’s best to use identically sized drives for RAID arrays to maximize reliability, performance, and efficient use of capacity.
Mixing Drive Models in RAID
Mixing different drive models from different brands in a RAID array can potentially cause compatibility issues. According to this Reddit thread, you should be okay as long as both drives present the same capacity to the operating system. RAID only looks at drive capacity and not the specific brand or model number.
However, according to this Linus Tech Tips forum post, mixing drive models can increase the likelihood of catastrophic failure, which is why enterprise environments often use a mix of drive brands and models. The consensus seems to be that mixing models is okay, but can introduce potential compatibility issues that may impact reliability or performance.
Overall, mixing drive models in RAID is possible but not always recommended. To minimize compatibility problems, match drives as closely as possible in terms of capacity, speed, cache size, and other specifications.
Conclusions
In summary, there are both pros and cons to using multiple drives in a RAID configuration. Some of the key pros include improved performance, capacity, and redundancy compared to a single drive. RAID 0 offers better speed while RAID 1 and 5 provide fault tolerance. However, there are also drawbacks like increased complexity, cost, and risk of total data loss if the RAID fails.
When it comes to mixing drive sizes or models in a RAID array, it is generally recommended to use identical drives to get the full benefits of RAID. Mixing drives can lead to unused storage capacity or performance bottlenecks. However, it may be acceptable to use different sized drives in certain RAID levels like RAID 5/6/10 as long as the minimum requirements are met.
In conclusion, using multiple drives in RAID can provide advantages over a single drive, but requires careful planning and configuration. For simplicity and predictability, identical drives are ideal, but mixing drives is possible if done correctly. Evaluate your specific storage needs and research the pros/cons of each RAID level to determine the best implementation for your situation.