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.
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SirKnobsworth - Thursday, March 13, 2014 - link
Thunderbolt 2 is really PCIe x4 + DisplayPort in disguise, and you don't need DisplayPort to your SSD.MrSpadge - Thursday, March 13, 2014 - link
Couldn't you build a nice M.2 to SATAe adapter in a 2.5" form factor and thereby reuse your existing M.2 designs for SATAe?Kristian Vättö - Thursday, March 13, 2014 - link
Technically yes, but the problem is that M.2 is shaped differently. You could certainly fit a small M.2 drive with only few NAND packages in there but the longer, faster ones don't really fit inside 2.5".Kevin G - Thursday, March 13, 2014 - link
"At 24 frames per second, uncompressed 4K video (3840x2160, 12-bit RGB color) requires about 450MB/s of bandwidth, which is still (barely) within the limits of SATA 6Gbps."This is incorrect:
3840 * 2160 * 12 bit per channel * 3 channels / 8 bits per byte * 24 fps ~ 896 MByte/s
And that figure is with with good byte packing. For raw recording, the algorithm may pack the 12 bits into two bytes for speed purposes meaning you'd need about 1.2 Gbyte/s of bandwidth. Jumping to 4096 x 2160 resolution at 12 bit color and 30 fps, the bandwidth need grows to about 1.6 Gbyte/s.
The other thing worth noting is that uncompressed recording is going to take a lot of storage. A modern phone recording at the highest quality settings with 64 GB of storage would last less than 40 seconds before running out.
Kristian Vättö - Thursday, March 13, 2014 - link
Oh, you're absolutely right. I used the below calculator to calculate the bandwidth but accidentally left "interlaced" box ticked, which screwed up the results. Thanks for the heads up, fixing...Kristian Vättö - Thursday, March 13, 2014 - link
And the calculator... http://web.forret.com/tools/video_fps.asp?width=38...JarredWalton - Thursday, March 13, 2014 - link
Aren't there *four* channels, though? RGB and Alpha? Or is Alpha not used with 12-bit?Kevin G - Thursday, March 13, 2014 - link
No real way to record with an Alpha channel value to my knowledge. Cameras and scanners etc all presume a flattened image as if everything were solid. The only exception to this would be direct frame buffer capture from video memory which can independently process an Alpha channel.Input media would generally be 36 bit. During the editing phase an Alpha channel can be added as part of compositing pipeline bringing the total bit depth to 48 bit. Final rendering can be done to a 48 bit RGBA file. Display output on screen will be reduced to 36 bit due to compositing for the frame buffer.
Nightraptor - Thursday, March 13, 2014 - link
When I saw the daughterboard Asus provided my instant thought was actually using this (in pcie 3.0 form) to somehow provide the option to add an external GPU to a tablet. I may be the outlier, but my dream would be to have and 11.6" 16:10 1920 x 1200 tablet with the ability to connect a keyboard dock to function as a laptop, or another dock with a discrete graphics card to function as a desktop for occasional gaming (1080p at high setting would be all I'd ask for - so pcie 3.0 4x should be sufficient). If you could somehow get a SATAe cable on a tablet I think this would do it.vladman - Thursday, March 13, 2014 - link
If you want speed from storage, get a nice Areca PCIe RAID controller, attach 4 or more fast SSDs, do RAID 0, and you've got anywhere from 1.7 to 2GB/s of data transfer. Done deal.