Performance Comparisons – Sequential and Random
905P sees a constant slight bump to write speeds across the board, rusing above the cluster of previous Optane parts. 970 PRO does take the crown at QD1 sequential, but this is partly due to the Samsung 3.0 NVMe driver doing a bit of DRAM write caching on the host.
The 970 PRO hands down wins on sequential reads. It gets a bit of a boost from its driver, but that doesn't matter – it easily exceeds 2.6GB/s with or without it.
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.
Random writes are difficult to gauge by this chart since we care about lower queue depths, and the results are all overlapping each other. Clearer results can be found on the next page for this one.
…and now we flip the script. Random reads require all of the work to be done before the IO can be completed, and the limit here at the more critical lower queue depths is NAND's read response time. NAND is the storage medium of all SSDs in this comparison, so we find them all starting at a similar range, with the ramp determined more by how many parallel flash dies are present.
For this chart, I've zoomed in a bit and shifted to a log scale so we can more clearly see the spread. In this zoomed view, it's clear that there are Optane drives, and then there are the rest, which all come in at close to 1/10th the random read performance. This is the limitation of NAND flash.