RAID (Redundant Array of Independent Disks) is a data storage technology that combines multiple disk drives into one logical unit. The main purposes of RAID are to provide increased data reliability and/or increased input/output performance compared to single drives.
There are several standard RAID levels that provide different combinations of features such as fault tolerance, performance, and capacity utilization. Two commonly used RAID levels are RAID 1 and RAID 5.
RAID 1 provides fault tolerance by duplicating all data across two or more drives. RAID 5 provides fault tolerance through parity data distributed across drives along with striping for improved performance.
This article will compare RAID level 1 and RAID level 5 in terms of reliability, performance, capacity utilization, cost, and ideal use cases to help determine which solution better fits specific data storage needs.
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. The different schemes or architectures are named by the word RAID followed by a number (e.g. RAID 0, RAID 1). A RAID setup increases performance and provides fault tolerance through redundancy.
According to the Cambridge Dictionary, RAID is defined as “a method of arranging hard disks so that if one of them fails, the computer can still continue working normally.” The goal of RAID is to provide protection against data loss in the event of disk failure, while also improving I/O performance for applications by distributing data across multiple disks.
RAID Level 1
RAID Level 1, also known as disk mirroring, is a fault tolerance configuration where data is copied in duplicate onto two or more separate drives (1). The drives contain exact copies of the same data, providing 100% redundancy in case one drive fails. With RAID 1, data can be read from either disk, improving performance. However, only one set of data is actually being stored, so there is no capacity gain over a single disk.
RAID 1 requires a minimum of two physical hard disk drives and writes data simultaneously to both drives. If one drive fails, the system can instantly switch to the mirrored drive with no interruption in service. This level provides good performance and excellent fault tolerance, but at the cost of only being able to use 50% of the total disk space for storage. RAID 1 is a good solution for anyone who needs a high level of redundancy and cannot afford downtime to recover from a disk failure (2).
RAID Level 5
RAID Level 5 (distributed parity) stripes data and parity information evenly across all disks in the array. This level provides fault tolerance and improves performance over a single disk, while also providing more efficient use of storage capacity compared to mirroring ([RAID 5 definition]).
With RAID 5, data is split into blocks that are striped and written across all disks in the array. An additional parity block for each stripe is calculated and also distributed across the disks. The parity blocks allow for error checking and recovery of lost data. If a disk fails, the parity blocks can be used to rebuild the lost data onto a replacement disk ([Standard RAID levels]).
A minimum of 3 disks are required for RAID 5. Since parity information is distributed, RAID 5 provides good performance for reads, as workload is balanced across many disks. However, write performance may suffer due to the parity calculation overhead.
[RAID 5 definition]: https://www.techtarget.com/searchstorage/definition/RAID-5-redundant-array-of-independent-disks
[Standard RAID levels]: https://en.wikipedia.org/wiki/Standard_RAID_levels
Comparing Reliability
RAID Level 1 offers full redundancy, meaning all data is copied to a secondary disk. If one disk fails, the data remains intact on the other disk. This provides very high reliability with full protection against single disk failure. Some implementations of RAID Level 1 offer triple mirrored redundancy for even greater fault tolerance.
RAID Level 5 offers single disk fault tolerance. The data and parity information is striped across all disks in the array. If any single disk fails, the parity information can be used to calculate and reconstruct the lost data from the remaining disks. This protects against data loss from a single disk failure. However, RAID Level 5 is more vulnerable than RAID Level 1 if multiple disks fail.
Overall, RAID Level 1 provides higher reliability with full redundancy. RAID Level 5 provides good protection against single disk failures, but lacks the full redundancy of a mirrored array. For mission critical data where uptime and data protection are paramount, RAID Level 1 is generally considered more reliable.
Sources:
https://techgenix.com/raid-1-vs-raid-5/
https://www.diffen.com/difference/RAID-1-vs-RAID-5
Comparing Performance
RAID level 1 and RAID level 5 differ significantly in their read and write performance characteristics.
RAID 1 provides excellent read performance since data can be read in parallel from multiple disks. Writes are slower in RAID 1 because data must be written to multiple disks before the write is considered complete. RAID 1 offers slower write speeds but could offer the same read performance as RAID 0 if the RAID controller uses multiplexing to read data from disks.
RAID 5 provides good read performance, although usually not as fast as RAID 1 since data is striped across multiple disks. The tradeoff is that RAID 5 offers much better write performance than RAID 1, since writes only need to be written to a single disk thanks to the parity disk. However, write performance does suffer compared to RAID 0 since the parity information needs to be calculated and written with each write operation.
In summary, RAID 1 has faster reads but slower writes compared to RAID 5. RAID 5 has good read speed and much better writes than RAID 1. For workloads requiring more reads, RAID 1 may be preferable. For balanced or write-heavy workloads, RAID 5 is likely the better choice for performance.
Comparing Capacity Efficiency
RAID level 1 has a 50% storage efficiency compared to the number of drives, while RAID level 5 has much higher storage efficiency. This is because with RAID 1, the data is fully mirrored across drives, so there is a 1:1 ratio of drives to available storage. For example, with four 1TB drives in a RAID 1 array, there would only be 2TB of available storage due to mirroring.
With RAID level 5, parity information is distributed across drives instead of fully mirroring. This means that if you have four 1TB drives in a RAID 5 array, you end up with ~3TB of available storage. There is some storage overhead due to the parity information (equivalent of 1 drive’s worth), but otherwise the bulk of the drives can be used for data storage. So there is much less wasted space compared to RAID 1 mirroring.
Overall, RAID level 5 is significantly more storage efficient than RAID level 1. RAID 5 can utilize the bulk of the drives for data storage, while RAID 1 effectively cuts the storage in half due to mirroring. If storage capacity efficiency is a priority, RAID 5 would be the better choice over RAID 1.
Comparing Cost
RAID level 1 typically has a higher hardware cost than RAID level 5 because it requires more disks to achieve the same amount of usable storage. With RAID 1, you need at least two disks to mirror the data, meaning the total raw capacity is double the usable capacity. For example, two 4TB drives in RAID 1 would give you 4TB of usable storage.
With RAID 5, you only lose the capacity of 1 disk to parity, so 5 x 4TB drives would give you 16TB of usable storage. However, RAID 5 requires additional read/write overhead for parity calculation that can impact performance. According to one analysis, this makes RAID 5 more expensive than RAID 1 for small arrays, but the cost advantage tips towards RAID 5 as the array size increases:
“RAID 1 vs RAID 5 – Difference and Comparison”
Overall, RAID 1 has a higher upfront hardware cost but avoids the parity overhead of RAID 5. For very large arrays where the cost of extra disks in RAID 1 becomes prohibitive, RAID 5 offers better overall value.
Use Cases
Choosing between RAID level 1 and RAID level 5 depends on your specific needs and priorities. Here are some key factors to consider:
High performance: RAID 1 will provide better read performance compared to RAID 5 since data can be read simultaneously from both disks. Choose RAID 1 for use cases that require very fast read speeds like transactional databases or virtualization hosting. [1]
Large capacity: RAID 5 is much more storage capacity efficient compared to RAID 1. With RAID 5, you only lose 1 disk worth of capacity vs 50% of total capacity with RAID 1. Pick RAID 5 if you need to maximize storage capacity. [2]
High availability: RAID 1 offers better redundancy and uptime since data is mirrored. If a disk fails, the other disk still has a full copy of the data. RAID 5 can only withstand 1 disk failure. For mission critical systems, RAID 1 provides higher availability. [3]
Budget constraints: RAID 1 requires at least 2 disks while RAID 5 can be created with a minimum of 3 disks. RAID 1 has a higher hardware cost. If budget is a major concern, RAID 5 provides adequate redundancy at a lower hardware cost. [2]
In summary, RAID 1 is preferable for performance focused applications where uptime is critical. RAID 5 offers efficient capacity with reasonable redundancy for scenarios where storage space and cost are constrained.
Conclusion
In summary, RAID level 1 and RAID level 5 offer different tradeoffs in reliability, performance, capacity efficiency, and cost. RAID 1 provides better reliability through mirroring, but has a big capacity hit. RAID 5 provides good reliability through distributed parity, while also delivering better capacity efficiency than RAID 1. However, RAID 5 can suffer performance issues with parity calculations and write operations.
For most use cases requiring redundancy, RAID 5 offers a good balance of reliability, performance, capacity, and cost. The distributed parity provides protection against drive failure without as much capacity overhead as mirroring. RAID 1 makes more sense for use cases needing the highest reliability with less concern for capacity efficiency. Overall, your specific needs around redundancy, performance, capacity, and budget will determine whether RAID 1 or RAID 5 is the better option.