Review: Samsung 840 Evo 750 GB SATA-3 SSD

Samsung unveils so-called 'entry level' SSD line with Pro speeds (July 25th, 2013)

MacNN Rating:


Product Manufacturer: Samsung

Price: $529 as reviewed

The Good

  • Ludicrous speed
    - High data density
    - Extremely low power demand

The Bad

  • SSDs still more expensive than hard drives
    - Long term reliability of TLC cells unknown

The consumer-grade solid-state drive (SSD) market is getting more crowded every day. There are drives of every capacity and speed, fitting nearly every budget and performance niche. Announced last week, Samsung is soon to ship the 840 Evo series of 2.5-inch SSDs. Immediately after the announcement, Electronista and MacNN Labs were given the opportunity to test one of the new large-capacity flash-storage drives. As the drive uses a new fabrication process and a few new advances, how does the drive measure up to its predecessors?

First off, the raw specifications from Samsung. All of the drives in the 840 Evo series have a sequential read speeds of 540MB per second, with write speeds varying from 410MB per second in the 120GB version, and up to 520MB per second in the 250GB capacity and larger. Random read and write speeds vary per model as well -- read speeds vary from 94,000 operations per second (IOPS), through 98,000 IOPS.

Write speeds range from 35,000 IOPS on the 120GB version through 90,000 IOPS on the 500GB-plus capacities. Cache spans from 256MB on the 120GB version through 1GB on the 1TB model. Samsung provided us the Samsung SSD 840 Evo 750GB version for testing, and we ran tests against its older cousins, the 840 Pro and the 830.

Modern SSDs are generally of three types -- SLC, MLC, and TLC. Single-Layer Cell (SLC) drives store one bit of information per cell on the SSD with very fast writes, where MLC stores two, and TLC stores three -- the latter with the best data density of all three products. SSD lifespan is measured per cycle of the individual cell, so a single bit flip in the three bits stored in a TLC SSD cell counts as a cycle. Therefore, all other factors ignored, the endurance of a MLC is less than that of a SLC, and the TLC is less than the MLC.

Manufacturers are somewhat reticent to declare the operational life of a SSD, but individual cells are generally thought to be around 5,000 program/erase cycles, with Samsung testing having passed 2,500 P/E cycles and still counting for the 840 Evo. So, unlike with a spinning platter hard drive which may rapidly fail, or may go for a decade or more depending on the manufacturing tolerances of the mechanical components of the drive, an SSD can be thought of having a "timer", per se counting down the life of the drive depending on how much writing -- rather than reading -- is done to the cells.

TLC-based SSDs haven't been around long enough for that much evidence to be collected regarding lifespan of the drive, but the general consensus is that the usable life of a TLC model is shorter than that of a SLC or MLC drive. Our recommendation, regardless of SSD architecture, is to acquire some of the monitoring tools available, OS depending, and periodic monitoring be performed on installed drives -- to say nothing of routine backups as with any other drive.

Beyond SSD media improvements, Samsung has boosted the controller on the drive as well: the new drive uses a three-core 400MHx MEX controller, up from 300MHz in the MDX used in the 840 and 840 Pro series SSDs. A new TurboWrite feature is used to boost speeds, primarily in the lower-specced smaller-capacity drives. When needed, the TLC cells are temporarily shifted to SLC mode, storing one bit per cell with the corresponding increase in write speed. When the drive is idle, then the SLC-stored data is moved to MLC cells. Samsung sees the most benefit to this in the smaller drives, with less cache than the larger models, but the feature is on every drive in the Evo line.

The drive is comparable, specs-wise, to the 840 Pro series -- the Samsung SSD speed champion, at least on paper. With larger files, the 840 Evo performs very close to the stated top speed, with our testing able to achieve peak speeds of 509.9MB per second with average speed not much lower at 498.8MB per second. Smaller data transfers, consisting of 100GB of MP3 files with an average size of 6.6MB, averaged 430.2MB per second with a peak of 466.9MB per second.

The same data transfer performed with the earlier Samsung 840 Pro SSD came in at 512.2MB per second peak, and 488MB per second average on large files. The MP3 move test averaged 439.0MB per second, with a peak of 474.8MB per second -- very similar results.

The 840 Evo has a form of thermal management as well, slowing transfer of the drive when it exceeds temperatures of 80C in an effort to protect the electronics of the device from early degradation or outright thermal failure. We lined the SSD with insulating material and allowed the temperature of the drive to increase to 82C. Sure enough, there was a dramatic decrease in speed, as expected. The large file transfer test dropped to an average at 310.2MB per second when the thermal protections kicked in, and the MP3 test averaged 302.0MB per second. The decrease in transfer rate cut the rate of temperature increase significantly, with the temperature of the drive stabilizing at 84C before it started falling just before completion of the hour-long test.

Increasing the duration of the thermal protection test, we found that the data transfer rate didn't start returning to its peak until the drive fell below 70C. Thus, the thermal management features of the SSD function as advertised. We expect that some laptops, especially those tailored towards gaming that run hot by design, would be a bad fit for the Evo SSDs because of this feature. Uninsulated, after an hour-long transfer, the external casing saw peak temperatures of 44.2C with an infrared thermometer, with the drive itself reporting internal temperatures of 45.8C.

Some nontraditional tests were performed with the drive. We disconnected the drive from its power and data while a large transfer was in progress, with no effect to the drive, other than the interruption of the transfer. We also cut power 15 times on a PC with Windows 8 running on it, with no apparent corruption or unrecoverable errors -- which SSD reputation suggests are more common on NAND media. While we weren't expecting any problems, we did perform some percussion on the drive casing while the drive was in operation ranging from mild taps with a pencil to decent whacks with a screwdriver handle, with no adverse effects other than some mild and shallow casing dents.

Less empirically, we liked the Evo drive. The fit and finish of the casing were sharp, with more of an eye towards design than is generally needed in a unit destined for internal fitting. The laptop migration kit includes a USB 3.0 to SATA data transfer cable as well as a spacer to allow the drive to fit in a larger compartment without "wiggle."

We used the Samsung-supplied data transfer cable for our own migrations with an assortment of tools in Windows 7, Windows 8, and OS X, and found the cable an excellent addition to the kit -- seemingly durable and well-constructed. Boot speeds on a late-model 15-inch MacBook Pro with the drive installed were excellent, with notable "wow" factor on reboots from fellow staffers and other passers-by when demonstrated.

The event at which Samsung released this series of drive was subtitled "SSDs for everyone." SSD adoption is rising, but until the price of NAND media drops significantly, we don't see them fully supplanting hard drives completely any time soon. The Samsung 840 Evo is a great start towards wide integration, particularly in the smaller sizes.

While large-capacity SSDs like the 750GB unit we tested are still not what one would call "affordable" for most users -- this unit retails for just under $600 -- the Samsung 840 Evo series is a step in the right direction for those who need both incredible speed yet also require large capacity. If you've got the money in your budget for these units, especially the larger capacities with more cache and rated for higher speeds, we do recommend them. But we would add a note of caution -- the TLC-based technology in the Evo doesn't have a long-term track record, so keep an eye on the accumulated stats of the drive over time.

by Mike Wuerthele


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