Understanding RAID Performance at Various Levels

Choosing a RAID level, one should consider many factors, including cost, reliability, capacity, and performance. It can be hard to understand how RAID works because it has different speeds depending on the level. But some rules of thumb apply to all levels for getting your head around it. In this article, we are going to explore RAID 0, 5, 6, and 10 and see how the performance of each of them differs from another.

RAID 0 is by far the simplest to set up because it has no overhead and power requirement. In essence, it is just two separate hard disks in a case. However, this also means that files can only be read or written to one disk at a time. There are no ’roundhouses,’ so reading and writing on both disks without waiting for each other consume all of them. The formula for write performance for RAID 0 is very simple: NX. RAID 0 is always the highest performing level. Let’s consider an eight-spindle RAID 0 as an example. When you take an individual drive (which can deliver 125 IOPS) and divide eight by 125, the amount of figure is 1,000 IOPS.

We included RAID 5 in this article because it’s a common and well-known type. But it shouldn’t be used in new systems. The latest technology is more efficient and user-friendly while still capable of providing the same level of reliability in data storage. There is no RAID 2, 3, or 4 levels found in production systems. Although RAID 5 is not recommended to use today, it is the foundation of other modern parity RAID levels; that’s why it’s important to know.

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This is a variation of RAID 5, which makes it safer, but also slows it down. Each writing operation requires the disks to read the data, read the first and then the second parity, and write the data for the first parity and then for the second one. This comes to the six-times write penalty. If we use our example, the formula that we get is NX/6, i.e., (8 * 125)/6, which comes out to ~167 Write IOPS or 1.33X.

RAID 10 is the second most basic RAID level, and it’s composed of a striped mirror of 2 sets. Compared to a simple RAID 0, which requires you to write the same data twice in order to create mirroring, RAID 10 cuts out that second write. The performance formula is NX/2 or .5NX.

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Another thing worth pointing out is that even the most complex fault-tolerant systems can suffer from a crash. Failures to correctly implement these systems lead to malfunction and data loss. Unfortunately, human error is a common cause when data is lost from a RAID. Data loss may happen due to reformatting, reinstallation, deleting, or overwriting a volume. These are human mistakes and not shortcomings of the technology used or the design of the array.