It's taken a decade, but SSDs are finally delivering. by Jeremy Laird
Solid-state storage was once the final frontier. It's arrival would banish the last remaining mechanised throwback and deliver us into a brave new age of lagless, lightning-quick computing. Back in 2008, when the first affordable SSD rocked up, initial impressions were revelatory, but it quickly became clear solid-state storage wasn't quite the instant fix – it turned out to be the most complex component of all.
Whether it's different data types delivering differing performance, drive survival or performance longevity, the more we learn, the more we recognise the limitations of earlier drives and realise how much potential there is. Fast forward to 2015 and today's SSDs are out-of-sight better than those laggy, stuttery early-adopter drives. If you haven't already jumped to SSDs, we guarantee you'll be delighted when you do. It's now more affordable, too. Decently capacious drives with great performance can be had for under £100.
But we can also see just how much more there is to do. Frustratingly, there are a number of emerging technologies which promise dramatic improvements in SSDs that have either already arrived but not yet delivered on their full promise, or remain tantalisingly out of reach.
What does that mean for you? If you already own a relatively up-to-date SSD, take it easy, you already have it pretty good. There's no hurry. If you haven't made the leap, the choice is trickier. You can either skip passing Go and collecting your £200, by heading straight for our reviews of the best current drives and experience a truly revelatory performance upgrade. Or you might want to find out about the next generation of drives and hold on that little bit longer. The choice is yours.
It's 2015 and the better part of a decade since the first mainstream solid-state drives appeared. But somehow, it still feels a little like SSDs haven't quite arrived.
For sure, all PC components just keep getting better, keep getting faster, keep getting cheaper, and SSDs won't ever get to a point where they can no longer improve. But today's SSDs are wonderful things already. It's all too easy to forget just how sluggish magnetic hard drives could make a PC feel. Once you go solid, you don't ever want to go back.
The problem is that the PC as a platform wasn't really ready for solid-state drives when they first arrived. It still isn't fully optimised for them even now. But that's about to change. When it does, we reckon the SSD will truly come good. Unfortunately, that change is pretty complicated and it's probably not going to be cheap. Oh, and it won't be a case of simply picking up a drive with a fancy new feature and plugging it in.
But let's start at the beginning. The problem with SSDs, it turns out, isn't just the SSDs themselves. It's your PC. Or more specifically, the standard storage interface inside your PC, known as SATA. The problem with SATA is twofold. Firstly, it doesn't have enough pure, dumb bandwidth. It's limited to a mere 6Gbps which translates into a real-world 600MB/s maximum.
Arguably just as problematic is that it doesn't know how to talk to SSDs properly. It uses a control protocol known as AHCI which was created for magnetic drives with spinning platters and never designed with SSDs in mind. And that means it introduces wholly unnecessary latencies into the read and write process in the context of SSDs.
Playing catch-up
What we need is a new control protocol optimised for SSDs. And that's exactly what we're getting in the shape of the NVMe or Non-Volatile Memory Express. NVMe isn't going to revolutionise the peak throughput you see. But what it should do is dramatically improve the random access performance SSDs can deliver. We're talking about all those little read and writes from your OS and apps, the ones that arguably have more impact on how responsive your PC feels moment to moment than peak sequential read and write performance.
Where things get really complicated, however, is the delivery vehicle for NVMe. You won't be surprised to learn it arrives alongside a new PCI Express-based storage interface, memorably known (not) as M.2. But it is confusing to learn that early M.2 SSDs have so far failed to support NVMe. Making matters even more complicated, there's an alternative new interface for SSDs, again with a PCI Express element, known as SATA Express, that weirdly looks stillborn. There's still the option of going with a straight PCI Express-based SSD too.
At first glance, then, the whole thing looks like a complete mess – a rats' nest of new interfaces, essential protocols not appearing in new drives and technology seemingly dead on arrival. So how is it all going to shake out? What kit will you need and what will the benefits be when it all comes together? The easy bit is that you can ignore SATA Express. Compatible sockets are fairly commonplace on new mobos but SATA Express drives are nowhere to be seen and the SSD makers we've spoken to typically say they've zero plans to produce them. Laters!
The remaining two are really variations on the theme, that theme being the high bandwidth PCI Express interface. M.2 is a standard that closely resembles the existing mSATA interface for mobile PCs and involves bare circuit boards with exposed memory and controller chips. That's a little odd in the context of neatly boxed SATA drives. And it also means you're only typically getting a single M.2 slot on a new motherboard. But in practice, it does make sense for the medium term as you're likely to only need a single M.2 drive for your OS and apps, leaving legacy SATA ports as more than adequate for mass data storage on bigger, fatter, cheaper drives.
Of course, the motherboard you have right now very probably doesn't have an M.2 slot. That means you'll either need a new mobo or a PCI Express adaptor card. In theory, the latter should allow for M.2 drives on legacy motherboards. In practice your mileage will vary. Some online research regarding your own specific make and model of mobo is the order of the day.
Express delivery
Assuming that's all sorted, the other major piece of the puzzle is making sure you've an NVMe-capable M.2 drive. We've had a fair few M.2 drives hit our test bench. But so far, none have support for NVMe. That's mostly because it's taking a little longer than anticipated for SSD controller chips with NVMe to hit the market. However, with the new Marvell 88SS1093 controller and others finally coming on stream, that's likely to change very soon. When it does, what can you expect in terms of performance?
Peak numbers will depend somewhat on configuration. Various PCI Express lane setups are possible, with x4 being the most we've seen referenced to so far. Whatever, what we're talking about is bandwidth in the low GB/s, the sort of numbers that were more typical for RAM just a few years ago, not hard drives. For us, however, the really intriguing numbers involve random access. Samsung has a new drive due out that's capable of 750,000 read IOPS. Admittedly this is an enterprise drive that's compatible with yet another interface standard known as SFF-8639 and which won't be coming to desktop PCs. But it hints at what NVMe drives will deliver. It's pretty much 10 times or an order of magnitude better than most of today's AHCI SATA drives. Yes, really.
While all this is going on, of course, the cost per GB of SSDs will keep dropping. Already, decent drives at what we think is the minimum desirable capacity – 240 to 256GB – can be had for well under £100. Admittedly, the unstoppable march that is Moore's Law and the process of shrinking transistors seems to have slowed. However, new approaches, including 3D NAND or stacked memory chips (see "What's a 3D SSD?", right) should keep prices tumbling and capacities increasing for several years to come. It's all good.