All of the drives on this chart deliver high sequential read performance, even those armed with TLC flash. Toshiba's Q300 Pro reads at nearly 500 MB/s with a queue depth of one. There's not much room to scale from there, if only because of the SATA interface's 6 Gb/s limit.
Writing quickly is more difficult for modern SSDs with large 128Gb memory dies. High-capacity models with 512GB or more of flash don't have the same problems as smaller drives; the greater number of dies composing them create more parallelization for absorbing the incoming data.
Even without a DRAM buffer, the Q300 Pro reports more than 500 MB/s at a queue depth of two. It trails some of the competition at a queue depth of one, though.
Random performance is where the missing DRAM affects performance. At a queue depth of one (the most important measurement point for client SSDs), Toshiba's 512GB Q300 Pro trails every other comparison drive, including two with TLC flash. Most enthusiasts don't use all of the random read throughput available to them, but the more you can leave in reserve, the better your latency will be in most cases. The Q300 Pro claws its way up the charts at higher queue depths, but continues to trail much of its competition through QD32.
We measured random write performance much lower than most of the field throughout the queue depth range, and the lack of a DRAM buffer is to blame.