Best SSDs of 2015 – what’s the best SSD on the market?

Solid-state storage used to be prohibitively expensive and hampered by tight capacities, but the market has recently matured. SSDs are now viable alternatives to hard disks, thanks to lower prices, higher capacities and faster speeds.

It’s a fast-moving part of the tech world, which means rapid innovation is the norm. The number of new techniques and technologies present in SSDs means there’s a lot to look out for when buying a drive – it’s certainly trickier than picking a hard disk.

Making memories

Flash memory chips form the bulk of an SSD, and advances in this space have the biggest influence on the performance and longevity of the drives you buy.

The most recent technological development was introduced by Samsung in May, in the shape of 3D V-NAND. This marks a big change in how SSD memory is constructed: instead of installing transistors in traditional horizontal layers, this drive stacks them vertically too.

This change means Samsung can pack in many more transistors without shrinking the manufacturing process, so the NAND doesn’t suffer from the performance inefficiencies, current leaks and higher costs associated with smaller process nodes. 

The 850 Pro employs a 40nm process – an archaic-sounding choice compared to the sub-20nm chips used in other commercial drives – but that’s moot when the Pro’s vertical arrangement means Samsung has the luxury of extra space.

This innovation means Samsung is finally free from the shackles of chasing smaller processes. That’s been the path of SSD development for several years, despite the obvious cons: smaller nodes mean better performance, but they put more demands on the components and reduce endurance. For those reasons, other firms including Intel are already moving down the same path to improve storage deficiencies.

Cell division

The flash memory in modern SSDs comes in three types: SLC, MLC and TLC. These acronyms describe the number of bits stored in the cells that make up NAND memory, with single-, multi- and triple-level used in different drives.

Each type of NAND has pros and cons. Single-level cells have the best endurance and raw speed, but they’re more expensive to produce, since each NAND cell stores only one bit, and thus storage density is lower. SLC SSDs are typically used for mission-critical PCs that read and write huge amounts of data.

The next step up, MLC, stores two bits per cell. This makes it cheaper to produce drives with the same capacity as an SLC equivalent, but longevity is hampered.

The increased number of bits in each cell means it’s more difficult to distinguish between the states, which reduces endurance: on an atomic level, higher voltages and more frequent changes in the charge level cause the silicon-oxide insulation inside the cells to erode at a faster rate.

Triple-level cells increase the capacity and reduce the cost even more, but performance and endurance decline further. These disadvantages mean MLC and TLC drives aren’t suitable for intense workloads, but they have ample endurance and performance for home and gaming systems – and generally, they’re cheaper. 

Flash memory controllers manage the interactions between the NAND cells and the rest of the PC. They don’t handle only file reads and writes – they also manage drive maintenance and cleaning procedures.

Many SSD manufacturers source controllers from third-party firms. Marvell is consistently popular, and controllers are often bolstered by custom firmware that allow for different areas of a drive’s performance to be emphasised.

Other firms develop their own silicon. Samsung produces its own triple-core MEX parts, and Intel also produces homegrown controllers.

Get connected

Every modern SSD uses the current SATA III standard to connect to your PC or laptop, and its maximum transfer rate of 6Gbits/sec is enough for consumer applications. But this is also on the road to change, and newer connectors could soon supersede SATA.

The most prominent currently is mSATA, which is already found inside many laptops and on most high-end motherboards. It’s a SATA III interface but, crucially, squeezed into a tiny space – the connector is slimmer than a SATA plug, and the drives themselves are several times smaller than normal SSDs.

Drives compatible with the mSATA standard are plentiful, but they’re still limited by SATA III’s maximum bandwidth – an issue that will become more significant as NAND chips become faster and cheaper.

A new form factor, M.2, solves this by cramming the SATA Express interface – which supports both SATA III and PCI Express 3 – into an even smaller connector.

Its maximum transfer rate of 16Gbits/sec outstrips SATA III, and M.2 drives can come in several different lengths and widths. If anything will replace SATA, it’s this.

How big?

That’s for the future, though. Assuming you’re buying today, the most important consideration may also be the most banal one: physical size. Most 2.5in SSDs sold these days are 7mm thick, but a handful are still the chunkier 9.5mm. These thicker drives may not fit inside laptops that only accept the slimmer parts. 

Take a peek inside the box, too. Some drives come with spacers to bulk out 7mm drives to fit into 9.5mm bays, and others come with adapters so they can be installed in a desktop PC’s 3.5in hard disk bay.

Also check the warranty. Some SSDs, such as Samsung’s 850 Pro, come with generous ten-year deals, but more affordable SSDs often make do with two or three years of coverage.

The final thing we’d check before buying an SSD is its endurance rating. Endurance is measured in gigabytes or terabytes, and these measurements represent how much data can be written to the drive before it’s liable to fail.

Endurance ratings in gigabytes generally indicate the amount of data that can be written to the drive daily, while a terabyte rating represents how much data can be written over the drive’s lifespan – its warranty period. 

These figures vary wildly. The cheap Crucial MX100 is rated for a modest 72TB workload, while the pricier Samsung 850 Pro is rated for 150TB.

Both of those figures are ample for typical consumer machines, but it’s worth paying attention in work systems that deal with intensive read and write processes.

What’s the best SSD on the market? Reviews

1. Samsung 850 Pro 256GB

Price when reviewed: £138 inc VAT

The market-leading Samsung uses innovative memory chips to devastating effect. Click here for the full review.

2. SanDisk Ultra II 240GB

Price when reviewed: £80 inc VAT

A keen balance between price and performance ensures this is an excellent budget drive. Click here for the full review.

3. Samsung 850 Evo 250GB

Price when reviewed: £110 inc VAT

A fine mid-range SSD from Samsung. Uses the same 3D V-NAND technology as the 850 Pro, but it is considerably cheaper. Click here for the full review.

Best of the rest

4. Fujifilm HQ-PC 256GB review

Price when reviewed: £108 inc VAT

Photography firm Fujifilm’s first foray into SSDs isn’t a homegrown part. It’s a rebadged Toshiba drive that employs 19nm MLC NAND. The HQ-PC put in an average display in most of the AS SSD tests, and its good performance in individual ATTO tests was undermined by mid-table speeds elsewhere.

In Anvil the Fujifilm’s 518MB/sec sequential read speed was reasonable, but its small-file performance suffered – in several of the tests we run it was well below average. The HQ-PC’s best performances came in the longer-term tests. Its Iometer result of 5,475 was close to the excellent Samsung 850 Pro, and its PCMark8 result of 4,991 was equally impressive.

Its £110 price is a lot to pay, though, for such inconsistent performance. A better mid-range bet is the Samsung 850 Evo.

5. Crucial MX100 256GB review

Price when reviewed: £80 inc vat

Crucial’s £80 drive works out at 31p per GB and, using that measure, it’s the cheapest SSD here; that low price hasn’t precluded innovation though. It’s the first mainstream consumer SSD to use 16nm NAND – no surprise given the drive is manufactured by Crucial’s parent company, Micron. It’s a double-edged sword, though, since the smaller process can improve performance but also cause inefficiencies.

The MX100 proved adept when reading files, but faltered when writing: in AS SSD’s read test its top 519MB/sec pace was this group’s second best, but its 332MB/sec for writes let it down. This pattern was repeated in ATTO, where the MX100 almost caught Samsung when reading, but fell behind when writing larger files. In Iometer its total I/O score of 1,754 was the group’s poorest.

The MX100 is cheap, then, but the SanDisk is almost as affordable and produced a more consistent set of results in our tests, so that’s our favourite value SSD.

6. AMD Radeon R7 SSD 240GB review

Price when reviewed: £110 exc VAT

This drive bears the AMD logo, but it’s made by Toshiba-owned OCZ. It uses a Barefoot 3 M00 controller similar to the chips inside OCZ’s SSDs, and Toshiba’s 19nm MLC NAND flash.

Its AS SSD sequential read pace was the worst here, and that poor form continued in ATTO – its read tests were among this group’s slowest. The R7 picked up in write tests: its AS SSD sequential write speed of 497MB/sec is the group’s third best. That write speed is hampered by inconsistency, though; in ATTO’s largest file-write test the R7’s speed of 533MB/sec is superb, but for the smallest files its performance is very disappointing.

Worst of all is the price, though: at £110, it’s poor value for money based on the performance on offer.