The Samsung EVO is spearheads a second-generation of solid-state drive to use the more affordable TLC flash chips. It allows an increase in capacity and reduction in price. And a surprise when it comes to performance. See all storage device reviews.
Samsung is still accelerating the development of flash memory, now introducing its second generation of TLC solid-state storage before any other brand has even shown its first. See also: Group test: what's the best SSD (solid-state drive)?
Three-layer cell (TLC) NAND flash can be a useful compromise to increase storage capacities and lower costs. But the 3-bit version of multi-layer cell (MLC) flash has an intrinsically slower write speed and shorter overall lifespan.
For better performance and longevity, there's still Samsung's 840 Pro Series with its more familiar two-layer MLC technology. But we found that in performance terms at least, the Samsung EVO can hold its head up high against the 840 Pro; and with it, all current leading SATA 6Gb/s solid-state drives.
Samsung 840 EVO 750GB: tender loving cells
The use of TLC flash has here allowed a long-awaited extension in storage capacities. As well as the familiar sizes of 120, 250 and 500GB, Samsung has added 750GB and 1TB sized drives.
The latter becomes the first truly terabyte SSD, since Crucial's competing flagship M500 series includes additional built-in over-provisioning that brings the available space on its largest SSD to just below the terabyte mark, at 960GB.
Recommended prices for the Samsung EVO Series SSDs start at £86.99 for 120GB, then £148.99 for 250GB, £289.99 for 500GB, £415.99 for 750GB and £509.99 for 1TB. Actual retail prices are likely to be lower when the SSDs go on sale around 5th August 2013.
Samsung EVO 750GB: Captain Slow, no
Samsung has developed a nifty way to compensate for 3-bit MLC's inherently slow write performance. The new addition in the EVO here is what Samsung's dubbed TurboWrite Technology. This overcomes the poorer write latency of TLC by treating a specially reserved write cache area of flash like SLC.
Single-layer cell flash was the first and fastest of its breed, and Samsung tells us it's found a way to emulate its performance using the same stock of TLC NAND – SLC and 3-bit MLC have the same physical structure, we were assured.
So incoming data is written to the TurboWrite buffer first at high speed... then rewritten to the main drive as and when convenient later.
The buffer size is relatively large, so that with most daily operations it should not be readily depleted. But if it is, it simply puts write operations back to regular TLC speeds. For reference, the original 840 Series with its unaided TLC flash had sequential write speeds of around 250 MB/s.
And since this dedicated part of the drive only works in SLC mode, Samsung assures us it will have better endurance than short-lived TLC – around 100 times longer life.
The two smallest drives each get 3 GB of TurboWrite Buffer, while the 500, 750 and 1000 GB capacity versions get 6, 9 and 12 GB respectively of fast-write buffer.
Samsung 840 EVO 750GB: Other changes
Besides some clever data juggling used to bolster write speed, several other changes have been noted for the Samsung 840 EVO when compared to the original 840 Series.
The controller is now designated MEX rather than MDX, still based on a three-core ARM processor and with clock speed increased from 300 to 400 MHz. This is said to assist in management of the larger capacities, as well as deal with the shift to a new 19nm NAND process.
We also understand that the controller now has more housekeeping automation hard-coded into it, rather than being programmed and run by firmware.
The controller is backed by more DRAM cache for the largest drives, taking 256 MB cache for the smallest 120 GB capacity, 512 MB again for the 250 and 500GB models; and now featuring 1 GB of LPDDR2 memory for the 750 GB and 1 TB capacity SSDs.
Idle power consumption is said to be reduced, while temperature sensing deliberately slows the drive down when it gets too hot under load. Dynamic Thermal Guard looks like a similar technology to the adaptive thermal monitoring used in Crucial's latest M500 series SSDs.
Samsung doesn't fully explain how the SSD is slowed down when it reaches over-temperature, only that the controller ‘reduces it power injection'. This automated attempt to prevent overheating is designed to reduce temperature when the drive hits 70 ºC.
Idle power consumption has been reduced, if only fractionally according to Samsung's figures, from 46 to 45 mW. Overall load power consumption figures have not been released. But given the way that Keun-Soo Jo, Samsung's senior engineer of memory product planning, was talking at the product's launch, this may have actually increased.
Although he did go on to suggest that the important metric is ‘power per performance'. Which is to say that power consumption under load may increase slightly, but the amount of data transferred in the same time will be much higher. So overall watts consumed per megabyte that's read or written may be lower.
It's comparable to Intel's new mantra, ‘the race to sleep', where short-term boosts to get the work done benefit overall energy consumption more than pressing for a longer process at reduced consumption.
Samsung 840 EVO 750GB: Performance
When we first lab-tested the Samsung 840 EVO, we were almost downcast to find comparable performance to the previous-generation Samsung 840 Pro. But we were not immediately aware of the technology inside, based on TLC flash like the cheaper 840 Series; not 2-bit MLC like the 840 Pro Series. Things were looking interesting again.
In fact in our lab tests it looked almost as if the 840 EVO has been tuned to replicate sequential read/write speeds of the 840 Pro: we recorded 516/498 MB/s for the latter, and now 510/490 MB/s for the new 804 EVO. That was using CrystalDiskMark in Windows 7.
Looking at the other extreme, of very small files, we found that 4 kB random reads had just about doubled in number, from 22 to 41 MB/s with the 840 EVO.
That's with a single queue, a good indicator for real-world performance still, as your PC spends a lot of time working randomly with many one-off small files, not just large sequential transfers or even multi-threaded small random read/writes.
Increasing queue depth to QD=32, the 840 EVO also approached its Pro-labelled mentor. Random 4 kB reads now hit 405 MB/s and writes were 367 MB/s. Which means the 850 EVO is now officially in the 100,000 IOPS league with its 104k IOPS read result.
Samsung 840 EVO 750GB: RAPID mode
Samsung had one more trick up its sleeve when it unveiled the 840 EVO Series. By acquiring the Nvelo company and its Dataplex software, it has developed an option within its Windows-only Magician software utility that speeds up performance even further. And not even by a particularly subtle delta either.
Real-time Accelerated Processing of I/O Data – or RAPID – is the backronym for Nvelo's intelligent ‘hot data' management, using more caching from DRAM than is normal in Windows, along with some compression techniques.
In our tests it certainly accelerated write performance, just as advertised. While sequential read speed was in a similar range – between 500 and 600 MB/s – our result from CDM showed sequential write speeds breaking four figures. To whit, regardless of data type the numbers settled on around 1050 MB/s sequential write.
That's around double what the SATA revision 3.0 bus (aka, SATA 6 Gb/s) can accomodate, so gives an indication that the clever work stands apart from the current SATA bottleneck.
Other impressive numbers that came out the end of our benchtesting with RAPID engaged include very fast 512 kB writes. These even exceeded the usual headline-grabbing sequential result, here hitting up to 1194 MB/s. And despite the RAPID magic relying to some extent on data-compression techniques, the results with random data in CDM at least were not affected – in fact while write speeds remained consistently over 1000 MB/s, the sequential read speed even increased, from 510 MB/s when writing 0x00 (zeroes), to 903 MB/s with random data.