Before we can compare the SSD 750 400GB to Samsung's SM951 512GB (AHCI), let's look at the two offerings from Intel. There is big capacity gap between the 400GB and 1.2TB models, and we're hoping Intel fills that space with an 800GB version. We think we've figured out why it isn't happening, though. The 1.2TB drive uses 18 channels and the 400GB model uses nine. Also, the 1.2TB model has a 4GB DRAM buffer, while the 400GB comes equipped with 2GB. An 800GB SSD 750 would likely break that perfect split. If an SSD doesn't have sufficient DRAM to buffer table data, then it suffers reduced performance. A theoretical 800GB model would most likely need a large 4GB buffer, which would have an adverse effect on cost. An in-between model in the SSD 750 family just might not fit Intel's pricing structure.
With half the number of channels from the controller to flash and half the DRAM, you might assume that the 400GB model's performance would suffer more than Intel's specifications suggest. But we were surprised to find that the company's numbers are spot-on; the nine-channel SSD 750 400GB only takes a moderate performance hit. Sequential read performance drops to 2200 MB/s, down from the 1.2TB model's 2400 MB/s. Sequential write performance drops a little further, sitting at 900 MB/s compared to 1200 MB/s.
The SSD 750 400GB also delivers high random IOPS throughput. It delivers a capacity class-leading 230,000 4KB read IOPS and 430,000 write IOPS. That performance is truly astonishing on paper. However, Intel's enterprise pedigree means you only get those numbers with lots of commands stacked up. Most users rarely achieve more than a queue depth of eight, so this is an area we'll have to explore in greater depth.
Intel's 400GB SSD 750 does have an advantage in one area over the 1.2TB model (besides price): it requires one-third the airflow over its heat sink. This makes the product better for small form factor systems that don't ship with large intake fans. In our testing of both SSD 750 models, we didn't run into any thermal issues, and we didn't add additional cooling.
This product series is the first client-based SSD to use the NVMe protocol. We covered NVMe in detail in our SSD 750 1.2TB review. If you missed it, you can read more about NVMe here.