In this article we will learn the logic behind the RAID capacity calculation. We will go through the calculation for all different types of RAID available.
What is RAID ?
To safeguard data in the event of a drive failure, RAID (redundant array of independent disks) allows the same data to be stored in various locations across several hard drives or solid-state drives (SSDs). However, there are several RAID levels, and not all of them aim to provide redundancy.
Use of RAID
The operating system (OS) perceives RAID arrays as a single logical drive. RAID improves performance by distributing data across several disks and permitting balanced input/output (I/O) operations. Redundant data storage further improves fault tolerance since employing many drives lengthens the average time between failures.
RAID uses disk striping or disk mirroring techniques. Mirroring allows data to be copied to several drives. Data can be distributed across several disk drives with the aid of striping partitions.
Before we start any of the Enterprise level OS Installation on the baremetal we do consider them having it on the RAID array rather than on individual disk. If you need support on OS Installation you may refer our Post on Rocky Linux 8 Installation
Different RAID Level
Different versions, or levels, are used by RAID devices. Six levels of RAID were defined in the original study that created the concept of RAID configuration and coined the term. IT professionals were able to distinguish between RAID versions because to this numbered approach. We will go through the majorly used RAID in the industry.
Let us now proceed towards understanding the RAID capacity calculation for different RAID Levels along with the example.
RAID 0
This RAID configuration only provides striping but no redundancy of data. hence this has the best performance, but it does not provide fault tolerance.
Calculation for RAID 0
Actually, neither the total number of disks nor the smallest disk size must be taken into account when determining the storage capacity of a RAID 0 array. The RAID capacity calculation here is simple and it adds all the drives inserted in the RAID array
Capacity = S1 + S2 + S3 + … + SN
Here, S is the size of the disk/drives
Example, if you have 3 disk of 2 TB each, the total capacity of the RAID array is 6 TB which is the sum of all the drives in the array.
Read & Write Speed
Although RAID 0 offers unmatched read/write speeds, it is not redundant, thus if one of the drives fails, all of the data in the array is lost.
RAID 1
This setup, which is often referred to as disk mirroring, uses at least two disks to replicate data storage. No striping is present. Because both disks can be read simultaneously, read performance is enhanced. Write performance is same to that of storage on a single disk.
Calculation for RAID 1
Since every drive has an exact duplicate of the data, RAID 1’s capacity is equal to the size of the smallest disk.
Capacity = Size of smallest disk
For example, if you have a setup of two disk each of 2 TB in a disk array the total capacity of the RAID 1 array will be only 2 TB as each drives mirrors the data from one another providing the data redundancy
Read & Write Speed
Because both disks can be read simultaneously, read performance is enhanced. Write performance is same to that of storage on a single disk.
RAID 5
Performance, fault tolerance, and cost effectiveness are all combined in RAID 5, one of the most widely used RAID configurations. The minimum number of drives required in this RAID is three where two of them is for data and the other one if for parity.
Calculation for RAID 5
A RAID 5 array’s storage capacity is determined by a number of parameters, including the number and size of disks.
Data and parity information are dispersed among the array of drives in RAID 5. In the case of a disk failure, the parity information is crucial for data reconstruction.
Following formula can be used to determine the capacity in RAID 5
Capacity = (N – 1) * S
Here, N is the total number of drive/disk and S is Size of Smallest Disk
The N-1 is the total number of data drives in the array excluding the parity drive. Here one of the key aspect is also the size of the disk/drive. Using the smallest disk size (S) guarantees uniformity because every drive in the array needs to be the same size. Hard disk space is divided into arrays by RAID controllers according to the array’s smallest drive.
For example, in a RAID 5 configuration with three drives of 500 GB, 1 TB and 2 TB, each drive has a maximum of 500 GB assigned to the array.
Let us better understand with few ore example and calculate the total storage capacity.
Take 5 Disk/drive in a RAID 5 array with each drive capacity of 1TB, 2TB, 4TB, 8TB & 10TB.
Here, total number of disk/drive is five hence N is 5 and the smallest disk out of the five is of 1 TB hence the value of S is 1 TB. With the formula in place we get the result:
Capacity = (5-1)* 1 TB = 4 TB
With 5 disk of multiple sizes but 1 TB being minimal the total storage capacity of RAID 5 is 4 TB
Read & Write Speed
There isn’t much of an advantage to write speed because the raid controller must perform parity calculations, but read speed has a maximum theoretical benefit of the factor of the number of drives minus one due to the parity data. It causes the writing process to lag.
RAID 6
RAID 6 is a powerful RAID configuration that offers outstanding data protection and fault tolerance. By integrating dual parity information across several drives, it builds upon the idea of RAID 5 and enables the array to survive the failure of up to two disks without losing any data.
Let us go through the mechanics of RAID capacity calculation for RAID 6 along with some example.
Calculation for RAID 6
With the addition of a parity drive, the RAID 6 storage capacity estimate is comparable to that of RAID 5. The entire number of drives and the size of the smallest drive must be taken into account in order to calculate the total storage capacity of a RAID 6 array.
The formula used to calculate the storage in RAID 6 is
Capacity = (N – 2) * S
Here, N is the total number of drives/disk in the RAID array and accordingly N-2 represents the number of data drives excluding the parity drives.
S represent the Size of the smallest disk
Suppose we have a RAID array with 6 drives with each of the drives size as 1TB, 2 TB, 4 TB, 7 TB, 8 TB and 10 TB. Here the smallest disk size is 1 TB hence value of S will be 1 TB
Capacity = (6-2) * 1 TB = 4 TB
Hence with 6 disk/drive in the array, minimum being 1 TB disk we have a total storage capacity of 4 TB in RAID 6.
Read & Write Speed
Because data can be read from numerous drives at once, RAID 6 improves fault tolerance and allows for quick data reading but the write speed is slower than RAID 5.
Conclusion
Hope with this article now you are comfortable in choosing the desired RAID for your environment. Now that you are expert on the logic and calculation of the RAID capacity for all different RAID level you will be able to quickly get through the exact storage capacity for most of the RAID level. There may be a situation where you will have to deal with multiple disk of different size for different RAID level so in that case there are multiple online capacity calculator available to get through the exact result.