Welcome to the wonderful world of M.2
To paraphrase Dr Evil, is it too much to ask for an M.2 drive with frickin’ laser beams, sorry NVMe support, attached to its head? No idea what we’re talking about? Let’s start at the beginning.
Solid-state drives were the final piece of the PC performance puzzle. Before they arrived, everything else was achieved with solid-state circuits. Central processing, system memory, graphics, the whole nine yards. But not mass storage of data.
No, that was still done using arcane magnetic platters rotating about a spindle and interrogated by read heads floating precariously above the platter surfaces. That made for slow going during certain tasks, most obviously collecting random bits of data from distant sections of the platters. It also makes conventional hard drives prone to failure due to the delicate moving components.
Of course in many ways those drives were, and remain, marvels of engineering. They were fundamentally a stop-gap idea waiting for a solution. That solution is solid-state storage where memory chips replace the magnetic platters. Suddenly, it doesn’t matter where the data is stored on the drive, it’s all equally accessible and, in the absence of moving parts with tight physical tolerances, you can knock things about to no ill effect. However, the arrival of the very first solid-state drives wasn’t quite the technical triumph we’d been expecting. Early drives suffered from some pretty epic performance inconsistencies and it quickly became apparent there was much work to be done before SSDs fully delivered on the theoretical promise of solid-state storage.
Nearly a decade later and the waiting isn’t quite over. Unfortunately, the new Samsung XP941 doesn’t change that. Surprised? After all, this is one of the very first SSDs to be based on the new M.2 storage interface. M.2, of course, makes use of the PCI Express interconnect and that means masses of beautiful bandwidth. Where existing SATA drives are limited to 6Gbps theoretical, which translates into about 550MB/s of real-world bandwidth, M.2’s PCI Express tech means whole gigabytes per second are possible. The specifics vary according to how many PCI Express lanes are commandeered for storage, but however you slice it, we’re talking about a huge leap forward.
For this particular drive, Samsung has configured four PCI Express lanes in 2.0 specification. On paper, PCI Express is good for 500MB/s per lane, so we’re looking at a ceiling of around 2GB/s for a four-lane drive or roughly four times faster than SATA 6Gbps. Of course, these are theoreticals and real-world performance will inevitably be lower. But it’s not bad from a single generational leap, eh?
Storage hunter
In fact, it’s so good that you’re probably wondering what on earth could be stopping this slick little memory stick from achieving storage nirvana. To find out, we have to dig down into the technical details a little.
The XP941 is an 80mm M.2 drive, making it the second longest in a four-strong range of standard M.2 form factors which also includes 42mm, 60mm and 110mm. This isn’t hugely significant for desktop PCs, as any motherboard with M.2 support should be able to cater for this drive physically. It’s worth noting for laptop PCs, however, where limitations may exist.
Anyway, the 80mm form factor is significant in allowing for up to eight NAND memory packages and that, in turn, is what allows the XP941 to hit the 512GB capacity tested here. For the record, Samsung is using its own 64Gb 19nm Toggle-Mode 2.0 MLC NAND. Still, it remains a very dinky little thing and, as jaded as we tend to be by even the most advanced kit, you have to marvel at the sheer storage capacity in such a small device. It’s quite magical.
Whatever, the XP941 uses Samsung’s first PCI Express SSD controller, the S4LNO53X01. If that doesn’t exactly trip off the tongue, there’s not much of a story to help you remember it either. Details are hard to come by which is probably a function of the XP941’s official status as an OEM product. In other words, it’s mainly intended for PC manufacturers to put in prebuilt systems rather than aimed at inquisitive punters doing DIY configs.
The best we can do is guestimate based on this drive’s specs that it’s probably a PCI Express version of the MEX controller that Samsung fits to the 840 Evo and other SATA SSDs. As for what those specs specifically are, we’re talking 1,170MB/s peak reads and 950MB/s writes. Random access, meanwhile, is rated at 122,000 IOPS for reads and 72,000 for writes.
Immediately, a few things become apparent. Firstly, this drive isn’t capable of maxing out its four-lane PCI Express specification. How much that actually matters given that it’s still claimed to be roughly twice as fast as any SATA drive is debatable. It’s also worth remembering that M.2 ports on Intel H97 and Z97 boards are in any case limited to two lanes. A more unambiguous issue is those random access numbers. They’re nothing special. And that, finally, brings us to Dr Evil’s head-mounted NVMe problem.
Compression session
For all its PCI Express prowess, this drive lacks support for the new NVMe storage control protocol. It’s an old school AHCI drive. And that means that like all other AHCI drives, it’s not truly optimised for solid-state memory. The upshot of all this is fairly predictable. This drive flies in sequential workloads. It puts out about 1GB/s for both reads and writes and tears through our 30GB file transfer test faster than any other drive here by a mile. It also looks pretty clever in the PC Mark consistency stress test, losing out only to the SanDisk Extreme Pro by that metric.
On the other hand, it kicks out some extremely mediocre-looking results in the AS SSD 4K random benchmarks and likewise doesn’t look remotely special in file compression workloads. All of which adds up to a pretty complicated way of explaining what was obvious from the get go. Without NVMe support, you’re not getting the full M.2 experience.
It’s also worth name-checking the caveats that apply to all M.2 drives. You’ll need motherboard support and that’s not a given. Only very recent mobos have native M.2 support and typically only cater for a single drive. Also, M.2 pinches PCI Express lanes. That can be a problem on the Intel LGA115x sockets with their limited PCI Express lane availability, especially if you’re running multiple graphics cards.
That said, most motherboards should support M.2 via a cheap PCI Express adaptor card, so the compatibility hurdle should be surmountable. It just may not be a case of simply hooking up the XP941 to your motherboard and letting rip. Finally, as we mentioned above, this is essentially an OEM product and that means it may not be too easy to find and source.
Ultimately, then, we’re a tiny bit frustrated by the XP941. It’s a big step forwards in terms of raw bandwidth, but misses out on the bit we’re really excited about, namely the big boost in random access performance promised by the new NVMe protocol. And that’s something we really want to see on any M.2 drive. It’s not like we’re demanding sharks with frickin’ laser beams on their heads, is it?