Introduction
Contents
RAID 0 Arrays
With the price of the SSDs dropping, you probably already thought about installing two SSD units on your computer and configuring them as a RAID 0 array, which, at least in theory, increases the performance of the SSD. But what is the real-world performance gain of such configuration? Does the stripe size affect performance? If so, what is the best number to use? These some of the questions we will try to answer in this article.
RAID means Redundant Array of Independent Disks (or Inexpensive, according to some sources). In RAID 0 mode, two (or more) drives are combined into a virtual drive that is seen by the operating system as a single unit. When data is stored, the RAID controller divides information sent by the computer in blocks (also called stripes) and spread them evenly across the drives available in the array, accessing each drive at the same time, in parallel. Because of this effect, performance (at least in theory) is multiplied by the number of drives available in the array. So, in a RAID 0 array with two drives, the performance is doubled (again, at least in theory).
The only drawback is that, if one of the drives fail, all data contained in the array is lost. So, RAID 0 is recommended when performance and disk space are more important than reliability. (With RAID 1 you can add additional drives to automatically copy the contents of one drive into another; you can combine the redundancy of RAID 1 with the performance of RAID 0 in RAID 10 and RAID 0+1 arrays, but we won’t be convering these configurations in this article.)
Part of the process of creating a RAID 0 array is to choose the stripe size, which is the size of the data block that will be used. Typically, this size varies between 4 kiB and 128 kiB.
Before proceeding, we highly suggest that you read our “Anatomy of SSD Units” tutorial, which provides all the background information you need to know about SSDs, and our tutorials “Everything You Need to Know About RAID” and “Does RAID0 Really Increase Disk Performance?,” which explain the basics on RAID arrays.
In our tests, we created a RAID 0 array with two identical PNY XLR8 120 GiB SSDs, each time with a different stripe size, and tested the performance of the array. We also tested the performance with a single SSD with no RAID configuration, in order to see the performance gain achieved by using a RAID array versus a single drive.
It is also important to keep in mind that in our case the RAID was controlled by the Intel Z97 chipset from our motherboard, and therefore a “software-based solution.” Results when using a dedicated RAID card, i.e., a “hardware-based solution” will likely be different.
Figure 1: the two SSDs used