Testing SATA Express And Why We Need Faster SSDs
by Kristian Vättö on March 13, 2014 7:00 AM EST- Posted in
- Storage
- SSDs
- Asus
- SATA
- SATA Express
Final Thoughts
While testing SATA Express and writing this article, I constantly had one thought in my head: do we really need SATA Express? Everything it provides can be accomplished with existing hardware and standards. Desktops already have PCIe slots, so we don't need SATAe to bring PCIe SSDs to desktop users. In fact, SATAe could be viewed as a con because it takes at least two PCIe lanes and dedicates them to storage, whereas normal PCIe slots can be used for any PCIe devices. With only 16+8 (CPU/PCH) PCIe lanes available in mainstream platforms, there are no lanes to waste.
For the average user, it wouldn't make much difference if you took two or four lanes away for SATAe, but gamers and enthusiasts can easily use up all the lanes already (higher-end motherboards tend to have additional controllers for SATA, USB 3.0, Thunderbolt, Ethernet, audio etc., which all use PCIe lanes). Sure there are PCIe switches that add lanes (but not bandwidth), and these partially solve the issue but add cost. And if you add too many devices behind a switch there's a high chance that bandwidth will become a bottleneck if all are in use simultaneously.
I'm just not sure if I like the idea of taking two, potentially four or six, PCIe lanes and dedicating them to SATAe. I'd much rather have regular PCIe slots and let the end-user decide what to do with them. Of course, part of the problem is that we're dealing with not having enough lanes to satisfy all use cases, and SATAe could spur Intel and other chipset to provide more native PCIe lanes.
For laptops and other small form factor builds SATAe makes even less sense because that's the purpose of M.2. 2.5" SSDs can't compete with M.2 in space efficiency and that is what counts in the mobile industry. The only purpose of SATAe in mobile that I can see is laptops that use 2.5" SATA drives by default that can then be upgraded to 2.5" PCIe SSDs. That would allow OEMs to use the same core chassis design for multiple SKUs that could then be differentiated with the form of storage and it would also allow better end-user upgradeability. However, I still believe M.2 is the future in mobile especially as we are constantly moving towards smaller and thinner designs where 2.5" is simply too big. The 2.5" scenario would mainly be a niche scenario for laptops that don't have an M.2 or mSATA slot.
This is how small mSATA and M.2 are
Another issue exists in the OEM space. There are already four dominant form factors: 2.5" SATA, half-height/length PCIe, mSATA, and M.2. With SATA Express we would need an additional one: 2.5" SATAe (PCIe). The half-height/length PCIe is easy because all you need is an adapter for an M.2 PCIe SSD like Plextor has, but 2.5" PCIe is a bit trickier. It would be yet another model for OEMs to build and given the current NAND situation I'm not sure whether the OEMs are very happy about that.
The problem is that the more form factors there are, the harder it is to manage stock efficiently. If you build too many units in a form factor that doesn't sell, you end up having used tons of NAND on something that could have been better used in another form factor with more demand. This is why M.2 and half-height/length PCIe are great for the OEMs—they only need to manufacture M.2 SSDs and the end-product can be altered based on demand by adding a suitable adapter.
Fortunately the inclusion of both SATA and PCIe in SF-3700 (and some others too, e.g. OCZ's upcoming Jetstream Express controller) helps because OEMs only need to build one 2.5" drive that can be turned into either SATA or PCIe based on the demand. However, not all controllers support this, so there are still cases where OEMs face the issue of an additional model--and even for those drives that do support SATA and PCIe, it takes additional die area and R&D resources, resulting in higher costs.
Ultimately I don't believe the addition of a new form factor is a major issue because if there is customer demand, the OEMs will offer supply. It may, however, slow down the adoption of SATAe because the available models will be limited (i.e. you can score a better deal by getting a regular PCIe SSD) as some manufacturers will certainly be slower in adopting new form factors.
All in all, the one big issue with SATAe is the uncertainty due to the lack of product announcements. Nobody has really come forward and outlined plans for SATAe integration, which makes me think it's not something we'll see very soon. Leaks suggest that Intel won't be integrating SATAe into its 9-series chipsets, which will push mainstream availability back by at least a year. While chipset integration is not required to enable SATAe, it lowers the cost for motherboard OEMs since fewer parts and validation are required. Thus I suspect that SATAe will mainly be a high-end only feature for the next year and a half or so and it won't be until Intel integrates it into chipsets that we'll see mainstream adoption.
Facebook
Twitter
RSS
131 Comments
View All Comments
Kristian Vättö - Tuesday, March 18, 2014 - link
Bear in mind that SATA-IO is not just some random organization that does standards for fun - it consists of all the players in the storage industry. The current board has members from Intel, Marvell, HP, Dell, SanDisk etc...BMNify - Thursday, March 20, 2014 - link
indeed, and yet its now clear these and the other design by committee organization's are no longer fit for purpose , producing far to little far to late....ARM IP =the generic current CoreLink CCN-508 that can deliver up to 1.6 terabits of sustained usable system bandwidth per second with a peak bandwidth of 2 terabits per second (256 GigaBytes/s) at processor speeds scaling all the way up to 32 processor cores total.
Intel IP QPI = Intel's Knights Landing Xeon Phi due in 2015 with its antiquated QPI interconnect and its expected ultra short-reach (USR) interconnection only up to 500MB/s data throughput seems a little/lot short on real data throughput by then...
Hrel - Monday, March 17, 2014 - link
Cost: Currently PCI-E SSD's are inexplicably expensive. If this is gonna be the same way it won't sell no matter how many PCI-E lanes Intel builds into it's chipset. My main concern with using the PCI-E bus is cost. Can someone explain WHY those cost so much more? Is it just the niche market or is there an actual legitimate reason for it? Like, PCI-E controllers are THAT much harder to create than SATA ones?I doubt that's the case very much. If it is then I guess prices will drop as that gets easier but for now they've priced themselves out of competition.
Why would I buy a 256GB SSD on PCI-E for $700 when I can buy a 256GB SSD on SATA for $120? That shit makes absolutely no sense. I could see like a 10-30% price premium, no more.
BMNify - Tuesday, March 18, 2014 - link
"Can someone explain WHY those cost so much more?"greed...
due mostly to not invented here is the reason we are not yet using a version of everspin's MRAM 240 pin, 64MByte DIMM with x72 configuration with ECC for instance http://www.everspin.com/image-library/Everspin_Spi...
it can be packaged for any of the above forms M2 etc too rathe than have motherboard vendors put extra ddr3 ram slots decicated to this ddr3 slot compatable everspin MRAM today with the needed extra ddr3 ram controllers included in any CPU/SoC....
rather than licence this existing (for 5 years ) commercial MRAM product and collaborate together to make and improve the yield and help them shrink it down to 45nm to get it below all of today's dram fastest speeds etc they all want an invented here product and will make the world markets wait for no good reason...
Kristian Vättö - Tuesday, March 18, 2014 - link
Because most PCIe SSDs (the Plextor M6e being an exception) are just two or four SATA SSDs sitting behind a SATA to PCIe bridge. There is added cost from the bridge chip other additional controller, although the main reason are the laws of economics. Retail PCIe SSDs are low volume because SATA is still the dominant interface and that increases production costs for the OEMs. Low order quantities are also more expensive for the retailers.In short, OEMs are just trying to milk enthusiasts with PCIe drives but ones we'll see PCIe entering the mainstream market, you'll no longer have to pay extra for them (e.g. SF3700 combines SATA and PCIe in a single chip, so PCIe isn't more expensive with it).
Ammohunt - Thursday, March 20, 2014 - link
Disappointed there wasn't a SAS offering compared 6GB SAS != 6G SATAjseauve - Thursday, March 20, 2014 - link
Awesome computerwestfault - Saturday, March 22, 2014 - link
"The SandForce, Marvell, and Samsung designs are all 2.0 but at least OCZ is working on a 3.0 controller that is scheduled for next year."When you say OCZ is developing on a PCIe 3.0 controller do you mean that they were working on one before they were purchased by Toshiba, or was this announced since they were acquired by Toshiba? I understand that Toshiba has kept the OCZ name, but is it certain that they have continued all R&D from before OCZ's bankruptcy?
dabotsonline - Monday, April 28, 2014 - link
Roll on SATAe with PCIe 4.0, let alone 3.0 next year!MRFS - Tuesday, January 20, 2015 - link
I've felt the same way about SATAe and PCIe SSDs --cludgy and expensive, respectively.
Given the roadmaps for PCIe 3.0 and 4.0, it makes sense to me, imho,
to "sync" SATA and SAS storage with 8G and 16G transmission clocks
and the 128b/130b "jumbo frame" now implemented in the PCIe 3.0 standard.
Ideally, end users will have a choice of clock speeds, perhaps with pre-sets:
6G, 8G, 12G and 16G.
In actual practice now, USB 3.1 uses a 10G clock and 128b/132b jumbo frame:
max headroom = 10G / 8.25 bits per byte = 1.212 GB/second.
132 bits / 16 bytes = 8.25 bits per byte, using the USB 3.1 jumbo frame
To save a lot of PCIe motherboards, which are designed for expansion,
PCIe 2.0 and 3.0 expansion slots can be populated with cards
which implement 8G clocks and 128b/130b jumbo frames.
That one evolutionary change should put pressure on SSD manufacturers
to offer SSDs with support for both features.
Why "SATA-IV" does not already sync with PCIe 3.0 is anybody's guess.
We tried to discuss this with the SATA-IO folks may moons ago,
but they were quite committed to their new SATAe connector. UGH!