Samsung 840 EVO 1TB SSD review

When it comes to SSDs it's all about sacrificing usable capacity for the speed of solid state storage, right? Well, with the Samsung 840 EVO 1TB they are looking to give you both size and speed without you needing to auction off your first-born for the privilege.

Yup, we're finally at a time in the evolution of the SSD where decent capacity drives are available to mere mortals. Previously, if you'd wanted a terabyte of solid state storage you'd have to go for a frighteningly expensive PCIe-based drive, like the KingSpec Multicore 1TB . That's retailing for as much as £2,300 / $3500.

Thanks to first Crucial, with their 960GB M500 , and now the Samsung 840 EVO 1TB, standard 2.5-inch 'terabyte-class' SSDs are finally within reach. We're talking around £500 / $650 for these drives, or close to 50p/65¢ per GB.

Okay, that's not exactly cheap, but definitely comparatively good value compared with the drives that have come before. It also means that, lower down the capacity stack, that value continues throughout the range.

How is this possible? Well, it's all come down to higher density NAND Flash chips and that fact Samsung manufacture everything from the NAND chips to the memory controller themselves. They're using their own 19nm 3-bit MLC NAND Flash chips, which offer higher capacity than with the 2-bit MLC chips they use on their top-of-the-line 840 Pro drives. That means the 840 Pro 512GB drive is the same price as the new 840 EVO 750GB. That's a full third extra, speedy, capacity for the same cash.

So, what's the difference between the Pro and EVO series? The Pro remains the top of Samsung's SSD pile thanks to its longer-lasting 2-bit MLC and the fact the entire capacity of the drive is capable of operating at its top speed no matter what. That's not something the 840 EVO can boast, as it has to implement some smart algorithms to ensure the performance of the EVO is up there with the Pro's quicker chips.

Samsung is calling this TurboWrite and it classes a certain amount of the drive's capacity as simulated SLC NAND. That enables the drive to write quicker to that area, essentially using it as cache. The speed stays at peak levels for as long as the simulated SLC isn't filled up. The drive will then flush the TurboWrite space into the slower areas of the SSD once it goes idle, but if the drive is continually used without letting the cache flush then it will revert to the slower 3-bit MLC speeds.

In this 840 EVO 1TB that's not really something you have to worry about too much as the TurboWrite cache is sitting at 12GB. You're unlikely to write more than 12GB to the drive in general usage, so performance is going to remain high for pretty much all the time you're using it.

That cache level doesn't stay so high for the rest of the range though. The 750GB drive has 9GB, the 500GB has 6GB and the 250GB and 120GB drives only have 3GB set aside for TurboWrite. While this means the 120GB drive has seriously impressive performance much of the time, it is going to be more likely to fill the cache on a regular basis.

Driving performance

So, what of performance then? Well, in a word: stellar. Obviously we're still limited by the stagnant-looking SATA 6Gbps interface, with its 600MB/s theoretical limit. That means, like pretty much every other 2.5-inch SSD around we're locked around the 520MB/s mark for sequential read/write performance. However, random performance has seen a great boost, dishing up double what previous drives have been capable of. The random 4K speed represents how quickly a given drive is capable of shunting around the small, bitty files that make up the bulk of operating system I/O operations. The quicker they're capable of doing this, the smoother the experience of using your rig will be. If your OS drive hits a snag somewhere that's when you get stuttering.

The new Samsung MEX memory controller in the 840 EVO is slightly higher clocked compared with the MDX of the 840 Pro series, and they have done some additional tweaks to ensure the random performance is high. And when I say high, I'm not messing around. In terms of write performance the quickest drives I've seen were knocking around 55MB/s, even the PCIe-based KingSpec could only manage around 60MB/s.

The Samsung 840 EVO will hit 110MB/s, making it the most responsive SSD I've ever tested. The random read performance also doubles, from just over 20MB/s to 41MB/s in the Samsung 840 EVO.

Head-to-head

For me, higher random performance is the holy grail for SATA 6Gbps-based drives. That's what's going to really impact your general system performance and responsiveness. It's this random performance that just gives the 840 EVO the edge over the competing Crucial M500 960GB drive. The M500 is slightly cheaper, but also slightly smaller - with a formatted capacity of around 890GB versus the 840 EVO's 931GB - and can't keep up with the faster Samsung drive in any of our performance metrics.

While at around the £500 / $650 neither of these drives are particularly affordable, it does mean that the price of the smaller drives in the range get more accessible. At £150 for the Samsung 840 EVO 250GB - which has almost identical performance numbers as the 1TB drive - you're really getting top-end performance, at decent capacities, for a great price.

Benchmarks

The £2,300 PCIe KingSpec drive is capable of some incredible peak sequential transfer rates, but its 4K random performance can't come close to what the Samsung 840 EVO 1TB can mange - at almost a fifth of the cost. These tests show just how quick the EVO, with its TurboWrite tech, is compared with the top-end 840 Pro series. Against the competing 960GB Crucial M500 it's no competition in the benchmark stakes.

Sequential read performance

AS SSD - MB/s: higher is better

Samsung 840 EVO 1TB - 515

Samsung 840 EVO 250GB - 515

Samsung 840 Pro 512GB - 520

Crucial M500 960GB - 496

KingSpec MC1S81M1T 1TB - 2122

Sequential write performance

AS SSD - MB/s: higher is better

Samsung 840 EVO 1TB - 503

Samsung 840 EVO 250GB - 504

Samsung 840 Pro 512GB - 500

Crucial M500 960GB - 440

KingSpec MC1S81M1T 1TB - 988

4K random read performance

AS SSD - MB/s: higher is better

Samsung 840 EVO 1TB - 42

Samsung 840 EVO 250GB - 39

Samsung 840 Pro 512GB - 26

Crucial M500 960GB - 23

KingSpec MC1S81M1T 1TB - 29

4K random write performance

AS SSD - MB/s: higher is better

Samsung 840 EVO 1TB - 110

Samsung 840 EVO 250GB - 106

Samsung 840 Pro 512GB - 51

Crucial M500 960GB - 62

KingSpec MC1S81M1T 1TB - 71