Performance Comparisons – Sequential and Random

Mid-pack performance on sequential writes and reads.

NAND SSDs are surprisingly fast at low QD random writes. This is for a few reasons. To explain better, let's review what happens when a typical NAND-flash SSD writes or reads:

  • Writes: Host sends data to SSD. SSD receives data and acknowledges the IO. SSD then passes that data onto the flash for writing. All necessary metadata / FTL table updates take place.
  • Reads: Host requests data from SSD. SSD controller looks up data location in FTL, addresses and reads data from the appropriate flash dies, and finally replies to the host with the data, completing the IO.

660p does ok on random writes since it is able to use its SLC cache (similar to other TLC SSDs). The important results will come at the lower queue depths, which are hard to discern with the above chart but will be more clear on the next page.

For this chart, I've zoomed in a bit and shifted to a log scale so we can more clearly see the spread. Despite this, the grouping is still extremely close, and the easiest way to view this more clearly is to shift to our QD weighted results (next page).

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