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2TB Samsung 850 EVO SSD, Singly and in 8TB RAID-0

Samsung 850 EVO 2TB SSD
(in drive sled for OWC Thunderbay 4 Mini)

Get Samsung SSD at

Thanks to B&H Photo for loaning four Samsung 850 EVO SSDs for testing and to for loaning the Thunderbay 4 Mini enclosure.

Update June 2018: see the reviews of the newer Samsung 860 EO 2TB and 4TB SSDs which are faster with much greater longevity.


The Samsung 850 EVO 2TB 2.5" SSD is a consumer-grade SSD whose huge capacity holds great appeal for those looking for a lot of fast storage. Laptop users, users of devices like the OWC Thunderbay 4 Mini, etc.

The 850 EVO is not an SSD designed to take a pounding 24X7 in a server environment or heavy usage environment, but rather as a device for storing a lot of data with very good performance. Its price and capacity are appealing for that purpose.

Of particular interest is using 4 X 2TB SSDs in the OWC Thunderbay 4 Mini as a RAID-0 stripe, thus achieving 8TB of extremely fast storage in a very small form factor—tests follow.

  • 2TB / 1.81 TiB capacity
  • Dimensions: 3.94 x 2.75 x 0.27" / 100.08 x 69.85 x 6.86 mm
  • SATA 6 Gb/s (compatible with SATA 3 Gb/s & SATA 1.5 Gb/s interface)
  • Samsung 32 layer 3D 3-bit V-NAND
  • Samsung MHX controller
  • TRIM Support
  • AES 256-bit Encryption (Class 0), TCG/Opal, MS eDrive IEEE1667 (Encrypted drive)
  • Power Consumption (max): Active Reads: 3.7 W, Active Writes: 4.4 W, Idle: 0.5 W
  • Reliability (MTBF): 2 million hours
  • Annualized Failure Rate (AFR) 0.45%
  • Reliability (TBW) 150 TBW / 80 GB
  • Uncorrectable Bit Error Rate: 1 sector per 1017 bits read
  • Operating Temperature: 32°F to 158°F / 0 to 70° C
  • Humidity: 5 to 95%, non-condensing
  • Data Retention 1 year power-off once SSD reaches rated write endurance at 104°F / 40°C

Controller and flash

The Samsung 850 EVO uses 3D V-NAND flash, which is not as robust as MLC flash. V-NAND technology was designed to handle a 40GB per day workload, which after ten years equates to 150 Terabytes written.

To put that in context, a single disktester fill-volume as shown here writes the entire drive (2000GB), and thus equates to forty (40!) days of rated use. Since the test was run three times just for the fill-volume test alone, that equates to 120 days of usage—in one day. As another example, saving a 4GB Photoshop file just 10 times a day equates to a full day’s usage, and yet your author (Lloyd) regularly saves files up to 10GB and often 5/10/20 files of size 2/4/5/6 GB each, and saves them several times typically. So 40GB/day rates usage is not a particularly durable design in terms of a Photoshop user who regularly works with big files. Still, most users are not likely to do nearly that much writing.

For professional users looking for the best durability, OWC is expected to debut a 2TB Mercury Extreme Pro 6G SSD in early 2016, with performance expected to be somewhat higher, but also with more durable MLC flash memory.


Samsung’s speed claims do not hold up to scrutiny in testing for any transfer size; see the test results which are much slower than suggested:

Access your data quickly and efficiently with the 2TB 850 Evo 2.5" SATA III SSD from Samsung. This 2TB solid state drive features sequential read speeds of up to 540 MB/s and sequential write speeds of up to 520 MB/s allowing for the rapid transfer of large files.


With a 2.5" form factor, this solid state drive is designed to be used in a variety of notebook and desktop computers. The reduced size is achieved through the use of Samsung's 3D V-NAND flash memory as each of the 32 cell layers are stacked vertically rather than horizontally. Samsung also implements their own TurboWrite technology to deliver enhanced sequential read and write speeds while Rapid Mode software utilizes the integrated cache (DRAM) memory to improve processing speeds. Insert this solid state drive into nearly any notebook computer and you benefit from improved battery life with the enhanced SSD controller allowing the drive to sleep at an efficient 2 mW.

Sustained transfer speed , single SSD

Performance testing by DiskTester, part of diglloydTools.
disktester fill-volume

The Samsung 850 EVO shows a good performance but still well below the read speed of the Micron P400E 400GB enterprise SSD, which itself is not a particularly fast SSD. Also, the Samsung 850 EVO is considerably slower than the OWC Mercury Extreme Pro 6GB 1TB SSD. In short, 2TB of capacity is its main feature, not maximum performance. But be sure to see the RAID-0 stripe results, where the Thunderbolt bus is the limiting factor.

Incompressible data was also tested with the same results—no difference in performance.

Sustained transfer speed of 2TB Samsung 850 EVO across entire 2TB capacity
in OWC Thunderbay 4 Mini, late 2015 iMac 5K

Transfer speed vs transfer size, single SSD

Performance testing by DiskTester, part of diglloydTools.
disktester run-sequential-suite -s 16K -e 512M --iterations 5 --test-size 4G

This is a good performance in context: SATA drives have more transaction overhead than the internal flash drives on the native PCIe bus. But it cannot compare to a PCIe flash drive as found in the iMac 5K and MacBook Pro Retina.

Perspective: the PCIe-based internal flash drive of the late 2013 Macbook Pro Retina delivers about 320-350 MiB/sec for 32 KiB transfers; it has a direct PCIe bus that lowers overhead. The 2015 MacBook Pro does far better, an incredible 700 MiB/sec for 32 KiB transfers. The late 2013 Mac Pro (Jan 2014 model, also PCIe) delivers only about 250 MiB/sec for 32 KiB transfers.

Transfer speed vs transfer size of 2TB Samsung 850 EVO
in OWC Thunderbay 4 Mini, late 2015 iMac 5K

4-way RAID-0 stripe

RAID- stripe performance was an OWC Thunderbay 4 Mini attached to a late 2015 iMac 5K with the RAID created using SoftRAID, 64K stripe size.

RAID-0 Stripe: Sustained transfer speed

Performance testing by DiskTester, part of diglloydTools.
disktester fill-volume [--fill randomblock]

Although the single-SSD speeds are not very impressive (see results above), the Thunderbolt 2 bus throttles performance such that a 4-SSD RAID-0 stripe offers maximal performance on large transfers as shown here. More cannot be asked of a Thunderbolt 2 solution in performance terms: 8TB of SSD storage that maxes-out the Thunderbolt 2 bus.

Write and read speeds for writing/reading zeroes (highly compressible) are seen to be identical to speeds with incompressible data. This is a boon to anyone storing images like JPEG, PSD, ZIP, audio files, etc, since these files are incompressible.

Sustained transfer speed of 4 X 2TB Samsung 850 EVO RAID-0 stripe, across entire 8TB capacity
in OWC Thunderbay 4 Mini, late 2015 iMac 5K

RAID-0 Stripe: Transfer speed vs transfer size

Performance testing by DiskTester, part of diglloydTools.
disktester run-sequential-suite -s 16K -e 512M --iterations 5 --test-size 4G

RAID stripe size 64K.

With a RAID-0 stripe, transfer sizes smaller than the stripe size run at single drive speed, as can be seen for the 16/32/64 KiB transfers. A RAID-0 stripe with 64K stripe size is no faster than a single SSD until transfer size reaches 128K. That is because with a 64K stripe size, it takes 128K to get 2 of the 4 drives fully involved, 192K for 3 drives, 256K for 4 drives.

With 256K transfers, speed picks up very nicely, but still is only a little more than half of peak performance, which requires 32 MiB transfers. Note that 90% of peak speed is reached with 4 MiB transfers.

Transfer speed vs transfer size of 4 X 2TB Samsung 850 EVO RAID-0 stripe
in OWC Thunderbay 4 Mini, late 2015 iMac 5K
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