![]() The latter can mean better drive efficiency, particularly in laptops and consoles. The former can improve lifespan and performance consistency by avoiding throttling. Other reasons include thermal and power management. Lower writes speeds may also induce less wear on the flash. The most obvious reason is to provide better performance consistency, that is sustained performance, particularly with a flexible pSLC cache. Samsung’s rated write performance of this flash has it faster than any other on the market, but there are reasons to limit write speeds. Post-pSLC performance may not seem super relevant in practice, but you are more likely to hit this state when the drive is fuller. This is slower than expected and, indeed, the rest of the drives in the test will all eventually out-write it. Hybrid caches are becoming more common and that’s generally a good thing as such caches offer a good balance between performance and consistency.Īfter the pSLC cache runs out, the 990 Pro maintains around 1.4 GBps in a direct-to-TLC mode. This drive may have different caching characteristics when run in PCIe 3.0 mode. The drive may engage in some folding in the background which can create an effectively larger cache. Of this, 10GB is static while 216GB is dynamic. Officially, the 990 Pro utilizes TurboWrite 2.0 - like the 980 Pro - which at 2TB is rated for 226GB. The 2TB Samsung 990 Pro writes at up to 6.2 GBps for 39 seconds, suggesting a pSLC cache size of about 240GB. We also monitor cache recovery via multiple idle rounds. We use Iometer to hammer the SSD with sequential writes for 15 minutes to measure both the size of the write cache and performance after the cache is saturated. Sustained write speeds can suffer tremendously once the workload spills outside of the cache and into the "native" TLC or QLC flash. Most SSDs implement a write cache, which is a fast area of (usually) pseudo-SLC programmed flash that absorbs incoming data. Official write specifications are only part of the performance picture. Sustained Write Performance and Cache Recovery Random read, low queue depth performance tends to be relevant for a drive’s “real world” feel, and the 990 Pro is the best we’ve yet tested here. The former result is not surprising given the relatively low read latency of this flash at 40µs, an area in which Samsung excels. Random performance is excellent with reads, particularly in Full Power Mode, but write performance is lackluster in both modes. The exception is at QD1, although performance is still relatively good. Controller handling here can lead to some unwanted inconsistency, although the real world impact is debatable.ĬDM’s sequential results indicate that the 990 Pro is better than the 980 Pro and generally it fares well. Samsung has moved to a four-plane design at 176-layer while at 128-layer it remained dual-plane SSDs actually open a superpage across all planes to improve performance. ![]() These variations are reversed at 1MB and 2MB, likely due to differences in the architecture of the flash. We do see some variation in the 990 Pro at higher block sizes, as we did with the 980 Pro.
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