RAID 5 versus RAID 10, HDD and SSD


RAID ArrayLet’s set some reference points upfront so that we can accurately discuss the differences between these two types of RAID arrays.

RAID Arrays

  • RAID 5 is a RAID ((redundant array of independent disks) configuration that uses disk striping with parity. As data and parity are striped across all of the disks, no single disk creates a bottleneck.
  • Conversely, RAID 10 combines disk mirroring and disk striping to protect data. RAID 10 requires a minimum of four disks, and stripes data across mirrored pairs. As long as one disk in each mirrored pair is functional, data can be retrieved. If two disks in the same mirrored pair fail, all data will be lost because there is no parity in the striped sets. RAID 10 provides redundancy and performance, and is the best option for I/O-intensive applications. One disadvantage is that only fifty percent of the total raw capacity of the drives is usable due to mirroring.

HDD

Raid 5 is less efficient on normal spinning hard disks (HDD) because it increases the number of random I/O operations. Writing small amounts of data more frequently results in slower performance than when writing larger amounts of data sequentially.

SSD

Conversely,  SSDs can write random smaller blocks of data more efficiently. What’s more important though is knowing the total amount of data written to the drive.

Parity

A parity drive is a hard drive used in a RAID array to provide fault tolerance. For example, RAID 5 uses a parity drive to create a system that is both fault tolerant and, because of data striping, fast. One way to implement a parity drive in a RAID array is to use the exclusive or, or XOR, function.

Striping

Disk striping is the process of dividing a body of data into blocks and spreading the data blocks across multiple storage devices, such as hard disks or solid-state drives (SSDs). A stripe consists of the data divided across the set of hard disks or SSDs, and a striped unit, or strip, that refers to the data slice on an individual drive.

Writing hard amounts of data to the array at once

With RAID 5, you’re not writing the data five times over – it’s actually 1.25 times in total with ¼ to each of four drives and the additional to the fifth drive for parity. This helps improve data recovery.

With RAID 10, all of the data is mirrored, so when using four drives, ½ of the available write bandwidth is utilized to store copies of your data.

Efficiency

RAID 10 is more efficient in that it’s able to keep the drives active (at a maximum) more so than RAID 5. However, for maximum performance (actual writing speed), RAID 5 is better because less time is used storing information that is redundant.

Workload variances

If you’re testing efficiency between these two types of RAID configurations, be aware that your results will vary depending on the type of test data you’re utilizing. A single threaded test will produce different results than say, running multiple simultaneous write threads.

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