RAID 5 is a storage configuration that combines block-level striping with distributed parity. It requires a minimum of three disks, with parity information distributed across all disks (Source).
With RAID 5, data is broken down into blocks and striped across all the disks in the array. The parity information, used for recovering lost data in case of disk failure, is also distributed across the disks. The distribution of parity provides fault tolerance and allows the array to survive a single disk failure without data loss (Source).
The main advantages of RAID 5 are increased read performance, ability to withstand one disk failure, and efficient storage capacity. However, write performance can suffer due to parity calculation and potential bottleneck from single parity drive. RAID 5 requires a minimum of three disks and is best suited for reads and situations where redundancy is important.
RAID 5 Architecture
RAID 5 distributes data and parity information across all drives in the array (typically 3-8 drives). The data is divided into stripes that are spread across the drives so that data is distributed evenly. Within each stripe, a dedicated parity block is calculated and written to a different drive in each stripe (University of Oklahoma, 2022). This provides redundancy in case a drive fails.
When data is written in RAID 5, it is broken into chunks and striped across the drives similar to RAID 0. Unlike RAID 0 however, for each stripe, a parity block is calculated using an XOR operation across the data blocks and written to a different drive within the stripe. This parity block can be used to reconstruct the data if a drive fails (DiskInternals, 2022).
For reading data, the requested data blocks are simply read in parallel from the drives since parity is not needed. For writes, new parity must be calculated and written based on the new data block values. This makes write operations slower than read operations.
RAID 5 Performance
RAID 5 performance is dependent on a number of factors including the number of drives, drive speeds, controller, and workload. In general, RAID 5 provides good sequential read speeds, but write speeds are slower due to the parity calculations.
For sequential reads, RAID 5 can achieve near linear scaling, so 4 x 1TB 7200RPM drives in RAID 5 can read at about 4 x 150MB/s = 600MB/s. However, writes are slower due to the parity calculation overhead. Each write requires the data to be written to disk, plus a parity calculation, so the total write performance is about the speed of 1 disk. With 7200RPM SATA drives, sequential write speeds are around 150MB/s for a 4 drive RAID 5 array (1).
For random I/O, RAID 5 struggles compared to RAID 0 or 10. The parity calculations significantly slow down small random writes. 4k random read speeds are decent, but 4k random write speeds may be as low as 5-30MB/s depending on the controller and drives (2).
There are several factors that can affect RAID 5 performance. Faster RPM hard drives or SSDs will provide better speeds. The controller plays a major role, with hardware RAID cards able to handle parity calculations much faster than software RAID. The workload also matters – large sequential reads/writes will see good performance, but heavy random I/O suffers compared to other RAID levels.
Overall, RAID 5 provides good sequential read speed combined with the redundancy of parity. But random write performance suffers compared to RAID 0 or 10. For write intensive workloads, RAID 10 may be a better option if the budget allows.
1. https://www.anandtech.com/show/8265/wd-red-pro-review-4-tb-drives-for-nas-systems-benchmarked/2
2. https://www.marcchesley.com/solid-state-drives-ssds-and-the-business-owner/
RAID 5 with 4 Drives
RAID 5 with 4 drives provides a good balance of performance and redundancy for many use cases. With 4 drives, read performance is generally very good as data can be striped across all drives. However, write performance suffers compared to RAID 0 or 10 due to the parity overhead.
Specifically, in a 4 drive RAID 5 array, each write requires 4 I/O operations – 3 writes for the data strips plus 1 write for the parity strip. This leads to a write performance penalty compared to RAID 0. However, read performance remains high since data can be read in parallel across multiple drives.
Overall, a 4 drive RAID 5 configuration offers significantly better redundancy than RAID 0 with moderately better performance than a 2 drive RAID 1 mirror. Many consider 4 drives to be the “sweet spot” for RAID 5 in balancing performance, capacity and redundancy for general purpose use.
According to benchmarks, maximum read speeds for a 4 drive RAID 5 array using 7200 RPM SATA drives can reach 400-600 MB/s depending on the controller and drives used. Writes are slower in the range of 200-400 MB/s.
Read Performance
With RAID 5 using 4 drives, read performance can be quite fast thanks to the striping and parallelization across multiple disks. According to this source, RAID 5 read performance with N drives is roughly N times the performance of a single drive for sequential reads. This is because data is striped across all disks, allowing reads to occur in parallel.
For random reads, performance is also boosted by striping but may not reach N times one disk. According to tests by ZDNet, 4 drive RAID 5 achieved up to 320 MB/s random read speeds, compared to 80 MB/s for a single drive. So parallelization provided a 4x boost but not the full 4x expected. Factors like disk array controller and CPU overhead impact random IOPS. Still, RAID 5 read speed with 4 drives is much improved over a single disk.
Write Performance
The write performance of RAID 5 with 4 drives depends on whether it is sequential or random writes. For sequential writes, RAID 5 can achieve up to 75% of the total disk write performance according to this source. This is because with 4 drives, the write operation requires updating the data and parity information across 4 disks. So the formula for RAID 5 sequential write speed with 4 drives is roughly 3X, where X is the sequential write speed of an individual drive.
For random writes, the performance of RAID 5 suffers more significantly. This is because random writes require reading the existing data and parity stripes, updating the new data stripe, and recalculating and writing the new parity stripe. This results in a minimum of 2 and up to 4 I/O operations for every random write. According to this analysis, the random write performance of RAID 5 is about 25% of a single disk or X/4, where X is the random write speed of a single disk.
Overall, RAID 5 write performance with 4 drives can vary significantly depending on the workload. Sequential writes achieve good throughput close to 3X. But random write performance suffers due to the parity calculations requiring multiple drive reads and writes. When optimizing RAID 5 performance, using drives with faster sequential and random write speeds can help overcome some of these limitations.
Factors Affecting Speed
There are several factors that impact the performance of RAID 5 arrays, especially when it comes to read and write speeds:
One key factor is the drive interface used. RAID arrays built with SATA SSDs will offer much faster speeds than those using HDDs. Upgrading to faster interface options like SAS or NVMe can also boost performance significantly. According to one source, “NVMe offers up to six times higher IOPS performance than 12Gbps SAS SSDs.”1
The RPM speed of the drives also impacts performance. Typical HDDs run at 5400 or 7200 RPM, while high performance models reach 10,000 or 15,000 RPM. Faster spinning drives reduce latency and increase throughput.2
The RAID controller plays a big role too. Hardware RAID controllers with dedicated processors and caching capabilities deliver much better performance than software RAID handled by the system CPU. Higher-end cards offer features like write-back caching, battery backups, and multiple processors to handle intensive workloads.3
Finally, stripe size configuration affects speeds. Larger stripes tend to improve sequential reads/writes while smaller stripes favor random I/O. Tuning this for your specific workload is important.
Alternatives for Faster Speed
While RAID 5 provides a good balance of redundancy and performance for many use cases, there are alternatives that can provide faster speed:
RAID 10
RAID 10, also known as RAID 1+0, combines mirroring and striping for both redundancy and increased performance. By mirroring two drives and then striping those sets in an array, RAID 10 provides the speed of RAID 0 with the redundancy of RAID 1. With 4 drives in RAID 10, you would have 2 mirrored pairs that are then striped. This results in faster read and write speeds than RAID 5, though less overall storage capacity. According to tests by ServeTheHome, RAID 10 with 4 drives can achieve sequential reads around 400-500MB/s and writes around 300-400MB/s, compared to 200-300MB/s for both on RAID 5 [1].
RAID 0
RAID 0 or striping spreads data evenly across all drives with no parity. This allows for maximum speed but provides no redundancy. RAID 0 with 4 drives can achieve sequential speeds over 500MB/s for both reads and writes. However, the failure of any single drive will result in total data loss. RAID 0 is best suited for temporary storage where redundancy is not required [2].
NVMe SSD RAID
Using NVMe solid state drives in a RAID array can provide substantial speed improvements over traditional hard disk drives. NVMe SSDs have much lower access latency and higher IOPS. Configuring these in RAID 0 or RAID 10 can achieve over 1GB/s sequential speeds. However, cost is significantly higher for NVMe SSD storage. This high-speed solution works best for applications requiring low latency and high throughput like video editing or scientific computing [3].
When to Use RAID 5
RAID 5 offers a balance of performance and redundancy that makes it a good choice in certain situations. According to EaseUs, RAID 5 is ideal for use cases that require:
- Medium to large storage capacity
- Redundancy to protect against single drive failure
- Decent read speeds
- Low cost per gigabyte
RAID 5 is commonly used for data storage and backup, email and database servers, and other applications that require high capacity without sacrificing too much performance. It offers fault tolerance without doubling the number of disks like mirroring.
According to TTR Data Recovery, RAID 5 is recommended for arrays with 5-6 drives. Larger arrays may benefit more from the double distributed parity of RAID 6. For smaller arrays where performance is critical, RAID 10 mirroring may be preferable.
Overall, RAID 5 provides a good balance of storage efficiency, performance, and redundancy for many mid-sized server and storage needs. It protects against single drive failures while still providing decent read speeds.
Summary
In summary, RAID 5 with 4 drives offers a balance of performance and redundancy. The specific read and write speeds will depend on factors like:
- The speed of the individual drives being used
- The interface connecting the drives (SATA, SAS, etc.)
- The RAID controller performing the parity calculations
In general, RAID 5 read speeds will be fast, since data can be read in parallel from multiple drives. Write speeds will be slower due to the parity calculation overhead. With 4 drives, RAID 5 write speeds are typically 3-4x faster than a single drive.
Compared to RAID 0, RAID 5 trades some write performance for fault tolerance. Compared to RAID 10, it offers more overall storage capacity but slower writes. For many applications where redundancy is needed but ultra-fast writes are not required, RAID 5 with 4 drives hits a sweet spot.
