Results: 128 KB Sequential Performance
Once again, we turn to Iometer to measure the most basic performance parameters.
Fantastic sequential read and write performance is a trademark of modern SSDs. To measure it, we use incompressible data over a 16 GB LBA space, then test at queue depths from one to 16. We're reporting these numbers in binary (where 1 KB equals 1024) instead of decimal numbers (where 1 KB is 1000 bytes). When necessary, we're also limiting the scale of the chart to enhance readability.
128 KB Sequential Read
Despite lower capacities and more aggressive pricing, San Disk's Ultra Plus excels in sequential reads. The Plus drives even contend for first place with a single outstanding command. At higher queue depths, every drive is locked in a massive SATA 6Gb/s dog pile.
When we break out SanDisk's drives from the comparative data, we can adjust the scaling to pick out more subtle differences between them. After several runs, the 128 GB model puts a bit of distance between the larger and smaller capacities, though that's just a few MB/s.
There is a bit (just a bit, mind you) more variance from one run to the next than you might expect, which could be an artifact of the nCache system. Regardless, we come away knowing that read performance isn't a weak point of these drives. At least not sequential reads. We'll look at random reads on the next page.
128 KB Sequential Write
The three Ultra Plus drives stack up much as you'd expect. The largest model peaks just under 450 MB/s, placing it among the most elite SSDs. SanDisk's 128 GB drive tops 280 MB/s, while the the 64 GB version falls just shy of 130 MB/s.
Scaling is smooth, too. Throughput doesn't increase based on outstanding commands, but rather with the addition of more flash. That's just SSD Architecture 101, though witnessing the tangible results helps put capacity into perspective. Size really does matter in this case.
When we drop in comparative data from other 240/256 GB-class drives, it quickly becomes apparent that the 256 GB Ultra Plus trades blows with the highest-end SSDs, while the mid-range 128 GB is merely competitive. The 64 GB Ultra Plus brings up the rear, enabling half the speed of the closest 200+ GB drive. That's not to shabby though, considering the only other 60/64 GB products offering similar write speeds do it with twice the die count (or are SandForce-based products working with easily compressible zero-fill data).
Near as we can tell, the Ultra Plus and Samsung 840 are pretty close competitors based on their performance and pricing. SanDisk's Ultra Plus gets the nod in sequential writes at 128 and 256 GB, but that's just one performance measure. The Ultra Plus has fewer memory channels at its disposal, while Samsung's three-bit-per-cell MLC (or TLC) leads to hobbled write speeds.
