Samsung SSD XP941 Review: The PCIe Era Is Here
by Kristian Vättö on May 15, 2014 12:00 PM EST
When SATA was introduced a bit over a decade ago, it provided major advantages over the old PATA interface. Not only was it faster and more power efficient thanks to the better signaling protocol, but the cabling was no longer big and clumsy with very limited length. It was no wonder that the industry quickly adopted SATA as the new interface for client storage and it has held its position throughout the years.
Since hard drives were the dominant storage media, SATA provided everything that the industry needed. The first generation SATA 1.5Gbps was already fast enough for the vast majority of use cases but about two years after the initial release of SATA, the second generation SATA was ready for prime time, doubling the throughput to 3Gbps. Even today's fastest hard drives can't fully saturate SATA 3Gbps, so there was obviously no rush to improve the interface as it already met the industry's needs. But that changed quickly around 2008.
The reason wasn't a sudden improvement in hard drive technology, but an emerging new technology that was based on non-volatile memory. We're talking about SSDs of course. The non-volatile memory part wasn't actually anything new as NAND has been around since the late 80s, but it was the first time NAND was being used in a PC form factor. Previously NAND had mainly been the choice for ultra mobile devices like MP3 players and phones but it was realized that the technology had the potential to be used in all computer-like devices, including PCs and servers. Since NAND was a solid-state semiconductor and it didn't have to rely on mechanical rotation, it allowed for much, much greater speeds. It's simply much faster to move electrons around a silicon chip than it is to rotate a heavy metal disk.
Obviously the first generation SSDs weren't all that fast and in many cases a traditional hard drive would still provide better sequential performance (although SSDs would destroy hard drives in a random IO workload). However, as the SSD companies learned to manage NAND and its characteristics better, the performance went up significantly. In 2009 we were already at a point where SATA 3Gbps was bottlenecking drives and a faster interface was needed to unleash the performance of NAND. Fortunately the Serial ATA International Organization (SATA-IO) had already released the standard for third generation SATA, which would again double the bandwidth to 6Gbps.
Crucial's C300
In 2010 we saw the first SATA 6Gbps SSD, Crucial's C300, make its appearance. Back then SATA 6Gbps wasn't integrated into chipsets yet and users had to buy a SATA 6Gbps PCIe card (or a motherboard with a third party SATA 6Gbps controller) to utilize the drive's full performance, but as soon as Intel was ready with their 6-series chipsets with native SATA 6Gbps support, every man and his dog came out with a SATA 6Gbps SSD.
But there was a problem. SATA 6Gbps still wasn't fast enough to meet the needs of SSD manufacturers as they were already able to saturate it. SATA-IO was given a difficult task: they would have to come up with a new standard with drastically better performance only a few years after the previous strandard had been announced. Not only would it have to be faster, but it also needed to be cost and power efficient. Instead of developing the SATA protocol further, which would have been expensive and time consuming, SATA-IO decided to utilize an existing interface found in every mainstream computer: PCI Express.
To allow backwards compatibility with the SATA interface, SATA-IO came up with two standards: SATA Express and M.2 (formerly NGFF). The idea behind SATA Express is that it routes PCIe and SATA 6Gbps signals to a single connector, which can then be used to connect either PCIe or SATA devices depending on the drive. It's mainly aimed at the desktop crowd and we did an extensive review of it just a while ago. M.2 on the other hand is the successor of mSATA and is electrically very similar to SATA Express. It also supports both PCIe and SATA 6Gbps signals, although ultimately it's up to the PC OEM to choose whether it will route both to the slot (i.e. you can have an M.2 slot with just PCIe or just SATA functionality).
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hulu - Thursday, May 15, 2014 - link
Second page of review, fourth paragraph, states they were only able to aquire the 512 GB version, since as an OEM product Samsung isn't sampling the drive to media.Always helps if you read the entire story before commenting!
JoyTech - Friday, May 16, 2014 - link
In that case, the reviewer better leave out the 128 & 256 GB out or mention the exclusions on first page, not 2nd page, 4th para; a good reviewer should make it easy for readers to access info, not act as lawyers and read the fine print!Also, I forgot to mention that their SSD bench marks have same problem (http://anandtech.com/bench/SSD/730), where they leave out Samsung SSD 840 EVO 250 GB, which is perhaps the best selling SSD in the market now. Very few people give a crap about 1 TB products, which is so proudly displayed in the bench!
Kristian Vättö - Saturday, May 17, 2014 - link
The first page is just an introduction with no mention of the XP941 anyway. It wouldn't have fit the context there and in the end I at least like to think that the reader reads the whole review and not just a paragraph or two. It's rather hard to write something for a reader who reads a part here and part there.As for the 250GB 840 EVO, it is in the bench but we haven't run Storage Bench 2013 on it. That's because the test itself takes around 24 hours to complete and with the strict review times we don't usually have the time to test all available capacities.
critical_ - Thursday, May 15, 2014 - link
Paradoxically, my problem with the M.2 form-factor is the number of sizes available to manufacturers. My Dell Venue 11 Pro tablet has a 2260 size 256GB SSD by Lite-On. There have been lots of firmware issues. The best thing would be to swap it out with a Samsung or Intel variant. However, there isn't much selection out there and 2260 is an oddball size. I'd like a 1TB mSATA SSD but it doesn't exist.Lenovo was smarter in this regard. Their Yoga 2 Pro uses the newer connector for the wireless card but the SSD is plain old mSATA. This allows me to pick from a variety of options without size concerns.
I know I'm ranting and it is still early in the M.2 game but I hope manufacturers settle on providing high capcities in the 2242 and 2260 sizes with plates (like half mPCI-E to full mPCI-E) to allow them to fit in bigger slots.
Babar Javied - Thursday, May 15, 2014 - link
Getting a smaller drive to fit into the bigger slot is easy. As you said, this can/should be easy with the use of "plates" or "expansion cards". So give it some time and you should have lots of options for your device. Should the 2260 size still remain an oddball, you can always get a 2242 size with extensions to help it fit into the bigger slotsdstarr3 - Thursday, May 15, 2014 - link
All due respect to the awesome performance the new interface promises, I still feel like it's going to be a while before the 6Gbps bottleneck makes my computer feel frustratingly slow.darwinosx - Thursday, May 15, 2014 - link
Read the benchmarks or ask someone who has been using PCIE SSD on a Mac for some time now. It's much faster and noticeable.Calista - Friday, May 16, 2014 - link
But also highly depending on what you're doing. Maybe most people are accepting a slight drop in performance in exchange for less issues with compatibility and the option of moving the drive to a second machine down the line or mounting it in a usb cabinet.Sabresiberian - Thursday, May 15, 2014 - link
I have 2 issues with PCIe as a storage interface, at this point in time.First is that, for me, as a high-end gaming PC user, the number of PCIe lanes to the CPU is already limited. SATA lanes are not since I simply don't use that many storage devices. The second is cost. A few weeks ago I bought 2 480GB Sandisk Extreme II's for $300 each, and just saw them for $260 each listed on Newegg - so, for less than the cost of a 512GB XP941 I can get around twice the storage at similar speeds if I install using RAID 0 using current high-end SSD devices.
Until Intel and/or AMD decides to provide more direct PCIe lanes and the cost comes down, PCIe SSDs are just an interesting upcoming technology, for me. :)
SirKnobsworth - Thursday, May 15, 2014 - link
At least on an Intel platform, you wouldn't normally be using lanes from the CPU for a storage device (which are usually dedicated to graphics) - you'd be using lanes from the chipset (of which there are usually 8).