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Samsung SM961 SSD Review

The SM961 is the SSD that everyone is talking about because it provides up to 3,200 MB/s of sequential performance. No more rumors, today we test the new Samsung SM961 1TB NVMe SSD from the SSI group. Is this your next SSD?

Real-World Software Performance

PCMark 8 Real-World Software Performance

For details on our real-world software performance testing, please click here.

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We spent an incredible amount of time testing our two SM961 1TB SSDs, and the PCMark 8 tests proved to be a real handful for this product. We expected much better performance from the SM961; it should have steamrolled the other products. We tested the drives with both Windows 8.1 and Windows 10 during our investigation. We also tested with two different Intel chipsets, the Z97 (Asrock Z97 Extreme6 with M.2 routed directly to the CPU) and the Z170 (Asrock Z170 Extreme7+ with M.2 routed through the PCH).

The SM961 didn't perform poorly in the real-world software trace tests, but we just expected more from the little fire-breather. Heavy sequential workloads allowed the drive to move to the top of the charts, but random workloads pushed the drive a little further down.

Here we see the performance from all of the tests combined. The SM961 only trails its 950 Pro brethren, but it enjoys a healthy lead over the other products.

PCMark 8 Advanced Workload Performance

To learn how we test advanced workload performance, please click here.

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The Samsung SM961 is impressive, but it may not be the best high-performance SSD for all of our readers. The drive delivers excellent burst performance, but over time, its performance slows (and almost wears down) as more data is stored on the flash.

We ran some additional tests with the drive half and three-quarters full to confirm some of our suspicions. The new Samsung 256Gbit MLC NAND reminded us of Micron's new 384Gbit TLC flash from the Crucial MX300 review. Both architectures share something new, and until now, the largest die size we've dealt with was 128Gbit. That's not the important part, though. The transition from 64Gbit to 128Gbit die density caused performance issues that SSD manufacturers eventually overcome by developing the larger capacity size SSDs that increased parallelism.

The SM961 uses just two packages with sixteen die per package. Samsung really should have spread the 32 die across four packages (instead of two) to increase the SM961's heavy workload performance. This would have increased the parallelism, and thus the sustained performance. The current SM961 architecture at this capacity size uses high-speed flash that delivers excellent burst performance, but the problem is that the controller is reading all of the data back through a limited number of channels.

Without getting too deep on a topic I've wanted to write about for a long time, we are also observing the SSD Yahtzee Effect. You can read more about it in this PDF from the Flash Memory Summit.

Total Access Time

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The SM961's high access time takes us down another road. The new 256Gbit die also increases the block size, which means the SM961 has to read, modify and write larger data sets. Couple that with what we discussed in the previous section and we can begin to understand why the SM961 has the highest random read performance we've ever tested, but does not surpass the 950 Pro under heavier workloads. 

Disk Busy Time

Not to pile on, but the SM961 1TB also has to work harder than the 950 Pro 512GB to complete the same amount of work. This carries over into the power consumption measurements. 

Notebook Battery Life

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The Samsung SM961 would deliver equal or better notebook battery life compared to the 950 Pro 512GB if the flash was the only component that mattered. That isn't the case, though. The memory configuration reels performance back in for this freshman 48-layer V-NAND product.

The single-sided form factor forced Samsung to take the SM961 to an extreme that we didn't expect. Most likely one or more of the major OEM customers, such as Lenovo, wanted the drive in a single-sided M.2 form factor to shave a few millimeters off a notebook. If Samsung spread the flash out to four packages we may have seen better performance in all of the real world tests today.

Chris Ramseyer
Chris Ramseyer is a Contributing Editor for Tom's Hardware US. He tests and reviews consumer storage.