RAID 5 arrays can vary greatly in size depending on the number and capacity of disks used. However, there are some general guidelines for how big a RAID 5 array can be:
Quick Answers
– A RAID 5 array requires a minimum of 3 disks.
– Total storage capacity is equal to (number of disks – 1) * (size of smallest disk).
– For example, a 3 disk array with 2 TB disks will have 4 TB of total capacity.
– RAID 5 arrays support up to 8 disks in consumer hardware and up to several hundred disks in enterprise gear.
– Maximum tested capacity for consumer RAID 5 is 32 TB with 8 x 4 TB disks.
– Enterprise RAID 5 arrays can scale up to petabytes of total capacity.
What is RAID 5?
RAID 5 is a storage technology used to protect against disk failures. It uses distributed parity, meaning parity data is spread across all the disks. This allows the array to continue operating even if one disk fails. The data from the failed disk can be rebuilt onto a replacement disk.
RAID 5 requires a minimum of 3 disks. It provides fault tolerance while also providing more overall capacity compared to RAID 1 mirroring. RAID 5 is a popular choice for network attached storage (NAS) devices, servers, and workstations that need large storage pools.
How RAID 5 Calculates Total Capacity
The total usable capacity of a RAID 5 array is calculated based on the number of disks and the capacity of the smallest disk. Here is the formula:
Total Capacity = (Number of Disks – 1) x (Size of Smallest Disk)
For example, take a 3 disk RAID 5 array with the following disks:
- Disk 1: 2 TB
- Disk 2: 2 TB
- Disk 3: 1 TB
The smallest disk is 1 TB. There are 3 disks total. Using the formula:
Total Capacity = (3 – 1) x 1 TB = 2 TB
Even though two of the disks are 2 TB, the total capacity is limited by the smallest disk. This demonstrates how RAID 5 capacity is dependent on the number and size of disks used.
Minimum Disks for RAID 5
RAID 5 requires a minimum of 3 disks in order to provide fault tolerance and capacity. With only 1 or 2 disks, it is not possible to implement distributed parity and recover from a failed drive.
With 3 disks, one disk’s worth of capacity is used for parity, leaving the remaining disks for storage. This allows the array to continue operating if any single disk fails.
While some RAID implementations allow you to create a 2 disk RAID 5, this is not true RAID 5. A minimum of 3 disks is required for the core RAID 5 design.
Maximum Disks for Consumer RAID 5
Most consumer RAID controllers aimed at home builds support up to 8 disks in a RAID 5 array. This includes RAID cards found in motherboards as well as add-on cards from vendors like LSI, Adaptec, HighPoint, and others.
8 disks is a practical limit for consumer use cases like gaming rigs, home servers, and desktop workstations. The largest consumer HDDs today are around 4-6 TB. With 8 of these disks, you can achieve RAID 5 arrays between 32-48 TB.
Here is an example 8 disk RAID 5 config with large consumer HDDs:
| Disks | Capacity |
| 8 x Seagate IronWolf HDD | 4 TB |
This setup allows for 32 TB of total capacity, enough for storing large media libraries and archives.
Maximum Disks for Enterprise RAID 5
Enterprise RAID controllers and chassis are designed to support many more disks than consumer hardware. Disk enclosures can fit dozens of hot swap bays, with connections for additional enclosures.
Enterprise-class RAID 5 implementations scale upwards of 100 disks in some cases. More commonly, large arrays are in the 12-24 disk range.
With high capacity enterprise HDDs now scaling to 16 TB and beyond, even relatively small enterprise arrays can reach hundreds of terabytes:
| Disks | Capacity |
| 16 x Seagate Exos HDD | 16 TB |
A 16 disk array with the 16 TB Exos drive achieves 256 TB of capacity while still providing RAID 5 redundancy. Truly enormous RAID 5 deployments at petabyte scale are possible for the largest data centers.
Ideal Disk Counts for RAID 5
While RAID 5 can work with as few as 3 disks and as many as hundreds of disks, most real world deployments sit in the middle ground. Here are some ideal disk counts for different use cases:
- Home media storage – 4 to 6 disk array provides good capacity while minimizing cost and complexity.
- Gaming PC – 6 to 8 disks balance performance and storage for active gaming data.
- Small office servers – 8 to 12 bay NAS devices with RAID 5 offer ample storage for businesses.
- High capacity archival storage – 16+ disks can achieve hundreds of TBs for archives and backups.
The complexity of managing larger arrays starts to outweigh the benefits beyond about a dozen disks for most use cases. Larger counts also increase rebuild times when a disk fails. Carefully choosing your disk count based on needs allows RAID 5 to shine.
Ideal Disk Sizes for RAID 5 Arrays
Disk capacity has grown rapidly in recent years. Consumer HDDs range from 1 TB to 6 TB per drive, while enterprise disks scale up to 16 TB and higher. With so many options, what is the ideal disk size for RAID 5 arrays?
There are a few guidelines to selecting disk size:
- Match disk specs – All disks should have similar performance and the same interface.
- Buy larger rather than more disks – Larger drives minimize the number needed.
- Consider rebuild times – Very large disks means long rebuild times.
Given the above, here are some ideal disk sizes for RAID 5 based on use case:
- Home NAS – 2-4 TB HDDs offer the best value and capacity.
- Business file servers – 4-8 TB HDDs balance price, capacity, and rebuild times.
- Media workflows – 8-12 TB HDDs provide massive storage.
- Archival storage – Use as large a drive as your bandwidth can support during rebuilds.
Carefully matching your disk size to the use case allows efficient RAID 5 arrays that avoid the downsides of undersized oroversized disks.
RAID 5 Performance
RAID 5 performance is heavily influenced by the number of disks in the array. More disks means better read performance but reduced write speeds.
For read operations, RAID 5 approaches the cumulative bandwidth of all disks. Data is striped across the disks, allowing reads to occur in parallel.
However, RAID 5 write performance is reduced compared to a single disk or RAID 0 stripe. Writes require parity calculations which add overhead. The more disks, the greater this overhead becomes.
In general, RAID 5 can achieve speeds of:
- 150-300 MB/s with 3 consumer HDDs
- 400-600 MB/s with 6 enterprise SSDs
- 1-2 GB/s with 12 NVMe SSDs
If extremely high write performance is needed, consider RAID 10 or RAID 01 which mirrors rather than parities data. But for general use, RAID 5 offers a good balance of speed and usable capacity.
Ideal RAID 5 Configurations
Putting together all the factors discussed so far, here are some example RAID 5 configurations well suited to different use cases:
Media Server and Backup
- 6 x 4 TB hard drives
- Total capacity: 20 TB
- HDDs balance price and performance
- Enough capacity for media libraries and backups
Gaming PC Storage
- 4 x 1 TB SSDs
- Total capacity: 3 TB
- SSDs provide excellent performance
- Enough capacity for a sizable game library
Business File Server
- 8 x 8 TB hard drives
- Total capacity: 64 TB
- HDDs keep costs down
- Tons of capacity for documents, files, shares
Archival Storage
- 12 x 12 TB hard drives
- Total capacity: 132 TB
- Massive high capacity storage
- Large drives keep disk count reasonable
Carefully tailoring the disk type, size, and number to your workload allows RAID 5 to deliver an optimal balance of redundancy, performance, capacity, and cost.
Conclusion
RAID 5 array size is highly flexible based on the number and capacity of disks used. At minimum, 3 disks are required with total capacity equaling the size of the smallest disk times one less than the number of disks.
Consumer RAID 5 implementations typically support up to 8 disks. Enterprise solutions can scale up to hundreds of disks and petabytes of total capacity. Ideal RAID 5 configurations choose disk count and size based on balancing performance, capacity, redundancy, and rebuild times for a particular workload.
When configured well, RAID 5 offers an excellent combination of usable storage, fault tolerance, and performance for a wide range of applications including home media storage, gaming rigs, business file servers, and enterprise data centers.
