Data redundancy refers to the practice of storing the same data in multiple locations. It involves creating duplicate copies of important data and storing them separately, often across different storage media or systems. Data redundancy is a key strategy used to protect against data loss and ensure high availability of critical information (https://www.techtarget.com/searchstorage/definition/redundant).
There are several benefits to building redundancy into a data storage infrastructure. Firstly, redundancy helps prevent data loss in the event of a drive failure, accidental deletion, file corruption, or physical damage to a storage system. If the primary copy of the data is compromised or destroyed, redundant copies ensure the data can still be accessed and recovered. Secondly, redundancy improves the overall availability and reliability of the data by allowing operations to continue even if one part of the system goes down. Finally, storing copies in geographically separate locations protects against site failures like fires, floods or other localized disasters (https://www.indeed.com/career-advice/career-development/what-is-data-redundancy).
There are some potential drawbacks to data redundancy like increased storage costs and complexities in synchronization. However, for mission-critical data, most organizations determine the benefits outweigh the costs. One way redundancy is implemented for storage systems is through the use of RAID technology.
What is RAID?
RAID stands for Redundant Array of Independent Disks. It is a data storage technology that combines multiple disk drive components into a logical unit. Data is distributed across the drives in one of several ways called “RAID levels”, depending on what level of redundancy and performance is required (TechTarget, 2022).
The different RAID levels each have their own characteristics and tradeoffs between things like speed, capacity, and redundancy. Some common RAID levels include:
- RAID 0 – Data is striped across drives for faster performance, but there is no redundancy.
- RAID 1 – Drives are mirrored for redundancy, but storage capacity is halved.
- RAID 5 – Data is striped across drives with parity information distributed across the array for redundancy.
- RAID 10 – Drives are mirrored and striped together, providing both performance and redundancy.
The goal of RAID is to increase reliability through redundancy, improve performance, or both. However, RAID is not a backup solution. The data is still susceptible to file corruption, malware, accidental deletion, or other issues. Regular backups are still necessary (Western Digital, 2022).
How RAID Works
RAID works by spreading data across multiple drives through a process called striping. Striping involves splitting data into blocks and distributing the blocks sequentially across all the drives in the array. For example, with a 4-drive RAID array, the first data block is written to drive 1, the second block to drive 2, the third block to drive 3, the fourth block to drive 4, the fifth block back to drive 1, and so on.
This striping mechanism provides performance improvements compared to a single drive, because multiple drives can be accessed in parallel for read and write operations. When data is requested, the RAID controller knows which drives contain the data blocks needed to fulfill the request. By accessing all drives simultaneously, throughput is increased.
Striping also provides redundancy and fault tolerance. If one drive in the array fails, the missing data blocks can be reconstructed from the remaining drives. For example, in a RAID 5 array with 4 drives, if one drive fails, the data on that drive can be rebuilt using parity information spread across the other 3 drives.
Overall, striping is the core mechanism that enables RAID arrays to achieve greater capacity, speed, and reliability compared to single drives. By distributing data across multiple drives in a balanced way, RAID improves performance while also introducing redundancy.
Benefits of RAID
There are several key benefits to using RAID technology for data storage and protection. The most notable benefits include:
Increased Redundancy
RAID allows data to be written to multiple disks simultaneously. This means there is built-in redundancy in case one of the disks fails. For example, in a RAID 1 array, the data is mirrored across both disks. If one disk fails, the data is still accessible from the other disk with no downtime or data loss (RAID definition).
Improved Performance
Certain RAID levels can significantly boost performance for read and write operations. For example, RAID 0 stripes data across multiple disks which allows for concurrent disk access. This means reads and writes can be performed in parallel, increasing overall throughput (A Guide to RAID).
Increased Storage Capacity
RAID allows multiple physical disks to be combined into one large logical drive. This can greatly expand the total storage capacity beyond what a single disk could provide. For example, a 4-disk RAID 5 array would provide the capacity of 3 disks worth of storage.
Disadvantages of RAID
While RAID offers important benefits like redundancy and improved performance, there are some downsides to consider as well:
Increased complexity – Implementing RAID requires additional hardware like a RAID controller, as well as configuration and management. This added complexity can make troubleshooting issues more difficult compared to single drives.1
Cost – There are additional upfront and ongoing costs associated with RAID, including needing to purchase extra drives. There is also the cost of a RAID controller.
Decreased usable capacity – Depending on the RAID level, the amount of usable storage capacity can be significantly lower than the total raw capacity of the drives. For example, in a 2-drive RAID 1 array, only 50% of the total capacity is usable for storage due to the mirroring.
Potential for downtime – If multiple drives fail at the same time, there can still be downtime required to restore the array. Regular monitoring and maintenance is required.
Slower write speeds – Write speeds may be reduced compared to a single drive, depending on the RAID level. Parity calculations in RAID 5/6 in particular can impact write performance.
RAID 0
RAID 0, also known as disk striping, spreads data evenly across multiple drives with no parity or redundancy (Wikipedia). It breaks data into blocks and stripes the blocks across all the drives in the array (TechTarget). The main benefit of RAID 0 is increased performance and disk throughput since data is written in parallel across multiple drives. Read and write speeds are faster compared to a single drive (Wikipedia).
However, RAID 0 provides no data redundancy or fault tolerance. If one drive in the array fails, all data will be lost. For this reason, RAID 0 is generally considered unsuitable for mission critical systems that require high availability (TechTarget). The large stripe size also means that RAID 0 is not well suited for uses requiring small read/write operations (Wikipedia).
RAID 1
RAID 1, also known as disk mirroring or disk duplexing, is a RAID configuration that creates an exact copy (or mirror) of a set of data on two or more disks (Wikipedia, 2023). This is done by writing identical data to each disk simultaneously. RAID 1 provides complete data redundancy but cuts the available disk space in half. For example, two 1TB drives in RAID 1 would only provide 1TB of usable storage.
Here’s how RAID 1 works: data is written to two identical drives at the same time. If one drive fails, the system can instantly switch to the other drive without any interruption in service. This provides high availability and fault tolerance. The failed drive can then be hot swapped for a new one, and the RAID system will mirror the data to the new drive after replacement (TechTarget, 2023).
The main benefits of RAID 1 include:
- Provides complete data redundancy in case of drive failure
- Allows for continuous operations if a drive fails
- Easy to recover data by replacing failed drive
The disadvantages of RAID 1 are:
- Only 50% efficient in disk storage utilization
- Requires at least two drives
- More expensive than single disk solution
RAID 1 is ideal for mission critical systems where downtime cannot be tolerated. It provides the highest level of fault tolerance compared to other RAID levels. The tradeoff is less efficient disk utilization.
RAID 5
RAID 5 is one of the most popular implementations of RAID that offers a great balance between data redundancy and storage capacity utilization. It requires a minimum of 3 drives and uses distributed parity, whereby the data and parity information is distributed across all drives (Standard RAID levels).
How RAID 5 works is that as data is written to the drives, parity information is calculated and written across the drives as well. If one of the drives fails, the RAID controller uses the parity data from the other drives to reconstruct the data that was on the failed drive (What is RAID 5?). This allows the array to continue operating normally even with a failed drive.
The main benefits of RAID 5 are:
- Good read performance since data is striped across multiple drives
- Only 1 drive worth of capacity is needed for parity, so high storage capacity utilization
- Can sustain 1 drive failure without data loss
The main disadvantages are:
- Slow write performance due to parity calculation overhead
- Not ideal for high write workloads
- Entire array is vulnerable during rebuild if another drive fails
Overall, RAID 5 offers a great option for redundancy while maximizing storage capacity for use cases that are not extremely write-intensive.
RAID 10
RAID 10, also known as RAID 1+0, combines both disk mirroring and disk striping to provide both performance and fault tolerance (TechTarget). This RAID configuration requires a minimum of 4 disks, with data being mirrored across pairs of disks and then striped across multiple mirrored sets (Acronis).
In RAID 10, data is written in stripes across multiple mirrored disk pairs. This provides high I/O performance and rapid response times from the striping, along with fault tolerance from the mirroring. If one disk in a mirrored set fails, the system can instantly failover to the other disk containing the same data. This provides high availability for critical systems (TechTarget).
The main benefits of RAID 10 include very high read/write speeds due to the striping, as well as high reliability from the mirroring. RAID 10 can withstand multiple disk failures so long as no more than one disk fails per mirrored set. The disadvantage is that RAID 10 requires more disks than other RAID levels, so it has a relatively high cost (Acronis). At minimum, RAID 10 requires 4 disks to create one mirrored stripe set. Most implementations would use more disks for additional stripe sets to increase performance and capacity.
Conclusion
RAID, or redundant array of independent disks, allows for the distribution and/or duplication of data across multiple drives to improve performance and reliability. There are several levels of RAID that offer unique benefits and drawbacks depending on the needs of the organization:
RAID 0 stripes data across multiple disks with no redundancy, offering fast performance but no fault tolerance. It’s best for non-critical data where speed is a priority.
RAID 1 mirrors data between disks, providing complete redundancy. It’s ideal for critical data where redundancy is crucial.
RAID 5 stripes data across disks with parity data distributed across the array. It offers a balance of speed and redundancy. RAID 5 works well for important data where some redundancy is needed.
RAID 10 combines mirroring and striping for fast performance and complete redundancy. It’s the optimal choice for mission-critical data where speed and redundancy are both essential.
The best RAID level depends on the priorities for performance, redundancy, and cost. Organizations must weigh their specific needs and use cases when choosing a RAID configuration.
