Results: 128 KB Sequential Writes
128 KB Sequential Write
This is where the analysis gets more complicated. When we tested SanDisk's Extreme II, our Iometer-based setup yielded specific, detrimental results. They weren't terrible, but we did notice that a larger-than-typical LBA range upset the drives. We suspect their behavior was attributable to SanDisk's nCache technology.
In the same way, the length of the testing at each queue depth means our results are stacked against the 840 EVO's maximum speed, penalizing the larger models due to their comparatively larger Turbo Write caches.
Take the 120 GB 840 EVO as an example. It should be hitting ~400 MB/s. But as I explained, it sets aside 9 GB of capacity to cache 3 GB of writes. Overflow is written to the remaining three-bit-per-cell memory at a slower rate. Samsung's 250 GB 840 EVO starts almost 100 MB/s faster. If we stopped this test after just a couple of seconds, though, you'd see throughput closer to 500 MB/s since the cache wouldn't be full yet.
The 500 GB and 1 TB versions can't quite hit the 500+ MB/s we'd expect because, again, we're exceeding the capacity of their respective caches. But more space set aside and additional parallelism facilitate results that come closer to Samsung's maximum specified Turbo numbers.
Somewhat unsurprisingly, the 120 GB 840 EVO butts up against the 250 GB 840. Samsung's older drive doesn't enjoy the faster controller frequency or on-drive caching. Those features help the 120 GB 840 EVO almost keep up with a vanilla 840 almost twice its size.
The 250 GB 840 EVO matches Intel's SSD 335 working on non-compressible data, and the two larger 840 EVOs nearly claim top positions through our test.
Samsung's Turbo Write technology propels the 120 GB 840 EVO into a spot between the 250 and 120 GB 840s. The 250 GB 840 EVO is sandwiched between a pair of Intel drives.
The 840 EVOs don't achieve their maximum numbers in our Iometer test, but 460 MB/s certainly isn't an outcome we'd dismiss.