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Samsung 850 EVO 250GB 3D V-NAND SSD Review

Samsung 850 EVO 250GB 3D V-NAND SSD Review
Samsung's three smaller capacity 850 EVO SSDs use the new MGX controller. Chris looks at the new controller, and gives us his thoughts on the 250GB model.
By: Chris Ramseyer | SSDs in Storage | Posted: Dec 8, 2014 9:05 pm
TweakTown Rating: 97%Manufacturer: Samsung





Earlier this morning, we tested and discussed Samsung's new 850 EVO 1TB SSD that uses 3-bit 3D V-NAND technology. The 1TB model is the only new EVO product to carry over Samsung's MEX controller from the 840 EVO and 850 Pro products. The 120GB, 250GB, and 500GB 850 EVO drives sport a new ARM-based controller we haven't yet seen.


New flash is paired with the new controller. The 850 EVO uses the same 3D V-NAND technology that first appeared in the 850 Pro, at least on the consumer SSD side. You can find a detailed overview of Samsung's 32-layer vertically stacked NAND in this article. What makes the 850 EVO's V-NAND different from the 850 Pro's V-NAND is the number of bits held in each cell. The 850 EVO stores three bits per cell, one more bit than the 850 Pro's two bits per cell. Of course, what we are talking about is the difference between multi-level cell (MLC), and triple-level cell (TLC) technology.



Specifications, Pricing, and Availability




The Samsung 850 EVO ships in four capacities, 120GB, 250GB, 500GB, and a large 1TB model. In this review, we will mainly focus on the 250GB, but we will also discuss the 120GB model in some places. The 120GB and 250GB 850 EVO products are very similar, much like the 500GB and 1TB models are similar.


Samsung's product specifications show us that the 250GB 850 EVO is capable of delivering up to 540 MB/s sequential read and 520 MB/s sequential write speeds. 4K random read performance is quoted at 97K IOPS, and 4K random write performance is up to 88K IOPS. Samsung is one of the few SSD makers unafraid of publishing random read QD1 performance data. With over 10K random read IOPS at QD1, we are not surprised since this is the tipping point that separates good SSDs from great SSDs.




Samsung's TurboWrite technology adds a SLC buffer layer to the flash. This takes place in the flash translation layer, which is a map of where data is stored on the SSD. The FTL can allocate data, telling a TLC cell to hold only 1-bit instead of three to increase the write transaction speed. Writing 1-bit is faster than writing three. The performance difference comes into play once all of the designated SLC-like area is full. At that point, the data needs to write to the drive in TLC mode, which is slower than SLC mode. The 850 EVO 250GB model writes sequential data at 520 MB/s in SLC mode, and 300 MB/s in TLC mode.


The random write performance also changes slightly in and out of TurboWrite. Inside the buffer zone, the 850 EVO 250GB writes 4K random data at 88K IOPS. Once the buffer is full, and the drive is forced to write to the TLC area of the flash, the performance drops to 70K IOPS.




The Samsung media guide for the 850 EVO shows us that Samsung is in line with our testing and evaluative thoughts on what makes a good consumer SSD. Samsung isn't afraid to publish low queue depth random performance, even though the market still likes to highlight high queue depth performance. The new MGX controller found on the 120GB, 250GB, and 500GB models was designed to deliver performance where most mainstream users need it, sequential and low queue depth random workloads.


All 850 EVO capacities support AES 256-bit full disk encryption, and work with eDrive, Waves, and other SED software suites. The 850 EVO also supports DEVSLP, a technology that lowers power consumption when the drive is idle, and increases notebook battery life. RAPID Mode also gets an update, and Samsung tells us to look for a near 2x performance increase in Windows start up, and application loading. Magician will update to version 4.5. You can see an overview of Magician 4.4 here. Samsung also includes Data Migration software that allows users to clone an existing drive to a Samsung SSD easily and quickly.




The 850 EVO 500GB and 1TB models match the endurance ratings of the 850 Pro. The 120GB and 250GB models have a TWB rating of 75 (TB of data that can be written to the drive). That comes out to 40GB a day, which is the same as the 840 EVO. Samsung did increase the warranty terms on the 850 EVO model to five years; the 840 EVO shipped with a three-year warranty.




Just prior to launch, Samsung sent over the MSRPs for the 850 EVO. The 250GB model will cost $149.99 at launch, and we don't expect to see a price drop until after Christmas, or possibly until as late as March 2015. A number of mainstream 256GB class SSDs currently sell for $109.99; a few even sell for less. The only SSD on the market at the time of writing that comes close to the 850 EVO's specifications is the Intel 730 Series 240GB, but the 240GB 730 lacks DEVSLP, and has a lower TBW rating. We can't recommend the 730 Series for notebook use since it pulls more power than a mechanical SSD. This leaves the 850 EVO in a class of its own at this price point.

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