Understanding Concept Of Striping, Mirroring & Parity

If you want to work as a Storage administrator or a SAN, NAS expert, then you should have good knowledge of some basic terms in storage and backup. Today we are going to talk about basic RAID levels, which you must understand.

As you must be knowing that RAID is the most widely used data protection technology that is used today and multiple disks work as part of a set to provide protection against HDD failures. Striping, Mirroring & Parity are the three basics of RAID levels, which we are going to discuss.

Striping, Mirroring & Parity

1. Striping:

For me, Striping is the most confusing RAID level as a beginner and needs a good understanding and explanation. We all know that RAID is a collection of multiple disk’s and in these disks, a predefined number of contiguously addressable disk blocks are defined which are called as strips and collection of such strips in aligned in multiple disks is called stripe.

Suppose you have hard disk, which is a collection of multiple addressable blocks and these blocks are stacked together and called strip and you have multiple such hard disks, which are place parallel or serially. Then such a combination of disks is called stripe.

Note: Without mirroring and parity, Striped RAID cannot protect data but striping may significantly improve I/O performance.

Online RAID 5 Calculator

2. Mirroring:

Mirroring is very simple to understand and one of the most reliable ways of data protection. In this technique, you just make a mirror copy of disk which you want to protect and in this way you have two copies of data. In time of failure, the controller uses a second disk to serve the data, thus making data availability continuous.

When the failed disk is replaced with a new disk, the controller copies the data from the surviving disk of the mirrored pair. Data is simultaneously recorded on both the disk. Though this type of RAID gives you the highest availability of data, but it is costly as it requires double the amount of disk space and thus increases the cost.

Recommended Article: Difference between RAID 10 & RAID 01

3. Parity:

As explained above, mirroring involves high cost, so to protect the data new technique is used with striping called parity. This is a reliable and low-cost solution for data protection. In this method, an additional HDD or disk is added to the stripe width to hold the parity bit.

Parity is a redundancy check that ensures full protection of data without maintaining a full set of duplicate data.

The parity bits are used to re-create the data at the time of failure. Parity information can be stored on separate, dedicated HDDs or distributed across all the drives in a RAID set. In the above image, parity is stored on a separate disk.

Recommended Article: RAID 5 vs RAID 6

The first three disks, labeled D, contain the data. The fourth disk, labeled P, stores the parity information, which in this case is the sum of the elements in each row. Now, if one of the Disks (D) fails, the missing value can be calculated by subtracting the sum of the rest of the elements from the parity value.

Hope you have understood the basic of these RAID levels. If you have any issues or concerns, please let us know through your emails and comment.