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One SSD Vs. Two In RAID: Which Is Better?

Results: 4 KB Random Read And Write Performance (Iometer)

Our Iometer benchmark demonstrates the link between queue depth and random read and write performance very well.

The bar charts below are indicative of average performance from a queue depth of one to 32. As you can see from the top measurement, 4 KB random reads, the two striped configurations are already dominating. Writes aren't as clear of a victory, though. The 512 GB 840 Pro manages to outmaneuver the two 128 GB SSDs, which themselves are only slightly faster than the single 256 GB drive.

A look at performance scaling over multiple queue depths is even more telling, though. Reads again appear bound by the NAND at low queue depths, only scaling in favor of RAID 0 once we apply plenty of parallelism. Writes are far more taxing, and two 256 GB drives barely beat one 512 GB SSD, while two 128 GB 840 Pros are just slightly faster than a 256 GB drive.