By Jeremy Laird on May 14th, 2015 at 10:00 pm.
All of this has happened before. All of it will happen again. I speak of the seemingly constant state of flux that afflicts the solid-state drive or SSD market. Well, that and my posts on SSDs which routinely predict an end game for SSD tech that somehow arrives and then starts all over again. First it was stuttering drives, then it was random versus sequential and compressible versus incompressible. Latterly, it?s PCI Express versus SATA. Whatever, it?s time to catch up on SSDs. Have they finally attained the glories of BSG up to season 1.5 (don?t argue, it?s down the pan from season two, episode 11)? Or are we still looking at the horrors of the final five? Let?s find out if anything has really changed and what the best buy is here and now.
To make this really simple for some of you who don?t care for the ins and outs, try this. Go buy a Crucial BX100 in either 250GB or 500GB trim depending on your budget. You?re done, catch you next time.
The Power of PCI Express
For everyone else, the big news with SSDs right now is of course the transition from SATA to PCI Express as the primary interconnect. But what does this mean?
In simple terms it means more bandwidth and in turn faster drives and snappier PCs. The fastest existing SATA interface tops out at 6Gbps in theoretical terms and roughly 550MB/s of real-world data throughput.
For PCI Express it?s all a bit complicated. Drives and indeed motherboards may support multiple PCI Express standards and in turn multiple PCI Express storage standards. Regards the latter I?m talking M.2, SATA Express and SFF-8639, the final two of which are mechanically identical but make different use of the available pins. Yup, it?s a bit of a nightmare.
This is the future of storage. Kinda
I suppose we are at least fortunate in that SATA Express appears to have zero traction in the form of drives you can buy. So it can be ignored for now. That leaves M.2 drives and SFF-8639 that require a dedicated connector on the motherboard or via an add-in card. M.2 drives are basically very small bare circuit boards, whereas SFF-8639 drives will come in 2.5-inch form factor and look essentially the same as existing SATA drives.
To that you can add what you might call pure PCI Express drives that simply plug into a PCI Express slot in the same manner as a graphics card. Again, I can only apologise for the sheer, brain numbing complexity of all these new SSD options.
Now, regards PCI Express itself, the fastest current spec is PCI Express 3.0 and that delivers 1GB/s per lane in each direction (ie in and out of the device in question). You can, of course, tag-team PCI Express lanes to generate more bandwidth.
I?m not clear if there is a theoretical limit to how many lanes an SSD could use. Obviously graphics cards and indeed motherboard slots max out at 16 lanes per slot and thus per device. Whatever, for the foreseeable future, it?s unlikely we?ll see drives using more than four lanes. Still, that?s a maximum theoretical throughput of 4GB/s or the sort of number that not too long ago looked healthy for the memory bandwidth of an Intel CPU.
It?s all about NVMe
There is, however, more to this PCI Express thing than raw bandwidth. There?s also the control protocol that allows your PC to talk to the drive. For SATA drives, that?s AHCI and it was never designed for use with solid state drives.
As I?ve mentioned previously, for PCI Express drives there?s a new protocol called NVMe which has been designed for solid-state storage and promises a major boost in the kind of random access work that makes your PC feel responsive.
It?s M.2. But is it NVMe?
If all of this sounds peachy, there are a couple of snags. Firstly, nearly all the PCI Express drives that have so far been launched have lacked NVMe support. And that makes them very unappealing.
Motherboard and CPU compatibility
Next up, Intel platforms of late have strictly limited PCI Express resources. I?m talking about chipsets and CPUs compatible with sockets including LGA1150, LGA1155 and LGA1156 and thus Sandy Bridge, Ivy Bridge and Haswell CPUs. In other words, CPUs like the Core i5-2500K, Core i7-3770K or Core i5-4670K. Anything remotely recent, then.
Anyway, those CPUs are limited to 16 native PCI Express lanes. In theory, you want all 16 for your graphics card. Take even one for an SSD, and your graphics will drop down to eight lanes. Now, it is debatable how much impact this will have. Indeed, it?s worth noting that eight PCI Express 3.0 lanes gives the same bandwidth as 16 PCI Express 2.0 lanes.
For a single graphics card in today?s games, as opposed to running multiple cards with Nvidia SLI or AMD Crossfire tech, it probably doesn?t matter. But if you are buying a PC to keep for a few years, maybe upgrade the CPU and graphics down the line, I?m less comfortable.
The two solutions to this are either go with Intel?s high end platform in the form of the X99 chipset and an LGA2011v3 chip like the 5820K, which have at least 28 PCI Express lanes. Or wait until later this year for Intel?s new mainstream Skylake CPUs on the LGA1151 socket (I know, it?s bloody confusing, but LGA1151 is yet another new socket) which get 20 PCI Express lanes and thus have four spare for storage.
And what of AMD?
As for AMD PCs, it?s a bit different as the PCI Express lanes are in the motherboard chipset, not the CPU. So the same limitations generally do not apply. PCI Express lane availability will vary according to motherboard. But even the entry-level AMD 970 chipset has 22 lanes. The top-end 990FX packs 38.
PCI Express adapter cards
Either way, unless you have a very new motherboard, it?s not going to have an M.2 or SFF-8639 connector. Adapter cards to drop into the PCI Express slots in your motherboard are available, however: something like this. How broad the compatibility is with cards like that and whether you?ll have any problems booting off it, well, I?m afraid I?m not clear. It?s early days with this stuff.
Nope, it?s not the stillborn Intel Larrabee graphics card. It?s a bleedin? big SSD
In any case, as I write, I?ve not personally had my hands on any M.2 drives with that crucial NVMe protocol support, so I?d recommend holding fire for now. Similarly, SFF-8639 drives for consumers as opposed drives designed for servers aren?t quite here yet. If you really want a PCI Express drive right now, therefore, you need to be looking to the likes of Intel?s NVMe-toting SSD 750 drive in plain PCI Express card format (as opposed to SFF-8639, which is announced but not yet available). It ain?t cheap, of course, current residing at just over £300 / $400 for the 400GB model.
The simpler SATA solution
For most of us, then, if you need an SSD immediately, it?s going to be an old school SATA drive. That?s not a disaster, especially if you are upgrading from an even more old school magnetic drive. It?ll be miles faster, it?ll be cheap and it?ll just work with pretty much any PC.
As for which SATA SSD to buy, given the coming PCI Express revolution, I lean toward cheapness with SATA drives. The advantages of the best and most expensive SATA drives look pretty piffling compared to what PCI Express drives deliver.
Thus, I?ll make this really simple, as per my comment up top. Go and get yourself a Crucial BX100. A 500GB model is roughly £150 / $200 (the 250GB model is about half the price). It?s not the best drive on the market, but it?s cheap and reliable and sidesteps any of the worries with drives like Samsung?s seemingly iffy TLC (triple-level cell) drives.
In other words, don?t fret about the previous 1,200 words or so. Just buy a BX100.
Oh and apropos of not all that much, isn?t it amazing to think that BSG reimagined first hit the small screen 12 years ago? Remarkable.