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
Testing SATA Express
SATAe is not commercially available yet but ASUS sent us a pre-production unit of the SATA Express version of their Z87 Deluxe motherboard along with the necessary peripherals to test SATAe. This is actually the same motherboard as our 2014 SSD testbed but with added SATAe functionality.
Test Setup | |
CPU | Intel Core i7-4770K at 3.5GHz (Turbo & EIST enabled, C-states disabled) |
Motherboard | ASUS Z87 Deluxe SATA Express (BIOS 1707) |
Chipset | Intel Z87 |
Chipset Drivers | 9.4.0.1026 |
Storage Drivers | Intel RST 12.9.0.1001 |
Memory | Corsair Vengeance DDR3-1866 2x8GB (9-10-9-27 2T) |
Graphics | Intel HD Graphics 4600 |
Graphics Drivers | 15.33.8.64.3345 |
Power Supply | Corsair RM750 |
OS | Windows 7 Ultimate 64-bit |
Before we get into the actual tests, we would like to thank the following companies for helping us with our 2014 SSD testbed.
- Thanks to Intel for the Core i7-4770K CPU
- Thanks to ASUS for the Z87 Deluxe motherboard
- Thanks to Corsair for the Vengeance 16GB DDR3-1866 DRAM kit, RM750 power supply, Hydro H60 CPU cooler and Carbide 330R case
The ASUS Z87 Deluxe SATA Express has two SATAe ports: one routed from the Platform Controller Hub (PCH) and the other provided by an ASMedia ASM106SE chip. The ASMedia is an unreleased chip, hence there is no information to be found about it and ASUS is very tight-lipped about the whole thing. I'm guessing we are dealing with the same SATA 6Gbps design as other ASM106x chips but with added PCIe pass-through functionality to make the chip suitable for SATA Express.
I did a quick block diagram that shows the storage side of the ASUS SATAe board we have. Basically there are four lanes in total dedicated to SATAe with support for up to two SATAe drives in addition to four SATA 6Gbps devices. Alternatively you can have up to eight SATA 6Gbps devices if neither of the SATAe ports is operating in PCIe mode.
Since there are no SATAe drives available at this point, ASUS sent us a SATAe demo daughterboard along with the motherboard. The daughterboard itself is very simple: it has the same SATAe connector as found in the motherboard, two molex power inputs, a clock cable header, and a PCIe slot.
This is what the setup looks like in action (though as you can see, I took the motherboard out of the case since inside case photos didn't turn out so well with the poor camera I have). The black and red cable is the external clock cable, which is only temporary and won't be needed with a final SATAe board.
The Tests
For testing I used Plextor's 256GB M6e PCIe SSD, which is a PCIe 2.0 x2 SSD with Marvell's new 88SS9183 PCIe controller. Plextor rates the M6e at up to 770MB/s read and 580MB/s write, so we should be capable of reaching the full potential of PCIe 2.0 x2. Additionally I tested the SATA 6Gbps ports with a 256GB OCZ Vertex 450. I used the same sequential 128KB Iometer tests that we use in our SSD reviews but I ramped up the queue depth to 32 to make sure we are looking at a maximum throughput situation.
There is no practical difference between a PCIe slot on the motherboard and PCIe that is routed through SATA Express. I'm a little surprised that there is absolutely no hit in performance (other than a negligible 1.5MB/s that's basically within the margin of error) because after all we are using cabling that should add latency. It seems that SATA-IO has been able to make the cabling efficient enough to transmit PCIe without additional overhead.
As for SATA 6Gbps, the performance is the same as well, which isn't surprising since only the connector is slightly different while electrically everything is the same. With the ASMedia chipset there is ~25-27% reduction in performance but that is inline with the previous ASMedia SATA 6Gbps chipsets I've seen. As I mentioned earlier, I doubt that the ASM106SE brings anything new to the SATA side of the controller and that's why I wasn't expecting more than 400MB/s. Generally you'll only get full SATA bandwidth from an Intel chipset or a higher-end SATA/RAID card.
The same goes for write performance. The only case where you are going to see a difference is if you connect to the ASMedia SATA 6Gbps port. I did run some additional benchmarks (like our performance consistency test) to see if a different workload would yield different results but all my tests showed that SATAe in PCIe mode is as fast as a real PCIe slot, so I'm not going to post a bunch additional graphs showing that the two are equivalent.
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Kristian Vättö - Thursday, March 13, 2014 - link
In theory two SSDs in RAID 0 should achieve twice the bandwidth of one. In practice that's almost true and you should expect maximum bandwidth of around ~1060MB/s (vs 550MB/s with one SSD).Exodite - Thursday, March 13, 2014 - link
External power, and we might get it as a *!*%?1* molex?Wake me up when we get to a usable revision.
grahaman27 - Thursday, March 13, 2014 - link
My thoughts exactly. I like sata, but this revision looks like a mess!invinciblegod - Thursday, March 13, 2014 - link
Why did they do translation between pci-express and sata in the first place? Was it because in the event of a pci-super-express SATA can just make new chips and the current hard drives would be compatible (like from PCI to PCI-Express)?npaladin2000 - Thursday, March 13, 2014 - link
I wonder if M.2 is the better solution here, and could be adapted to serve the enterprise niches that SATAe is aiming for? After all, it provides the direct PCIe interface, and also provides power and is a small connector.SirKnobsworth - Thursday, March 13, 2014 - link
For bigger, higher performance SSDs I think that actual PCIe cards are going to remain dominant. M.2 provides an x4 interface but the highest performance SSDs will have no trouble maxing that out. I think we may have already seen x8 cards demoed but I'm not sure.Veramocor - Thursday, March 13, 2014 - link
Could a internal motherboard USB header be used instead? USB 3.1 does about 10 Gpbs (with overhead) and would supply power. The cabling would be much cleaner.Or an internal Thunderbolt 2.0 connection does 20 Gbps. Imagine a single internal wire supplying both power and data instead of the mess this looks like. It would beat the speed of everything save PCIe 3.0 x4.
Kristian Vättö - Thursday, March 13, 2014 - link
USB has massive overhead. USB 3.0 manages only around 280MB/s in real world, whereas the theoretical maximum is 625MB/s (5Gbps). That is over 50% overhead! Assuming similar overhead, USB 3.1 would do 560MB/s, which is inline with SATA 6Gbps. However, USB uses CPU a lot more, making it very inefficient.As for Thunderbolt, it's basically just cabled PCIe. The difference is that TB requires expensive controllers and cabling to work, whereas PCIe alone is much cheaper.
I think SATA-IO just needs to get back to the drawing board and get rid of the external power requirement. PCIe supplies power, so there really shouldn't be need for more than that.
phoenix_rizzen - Thursday, March 13, 2014 - link
Just make a PCIe x2 connector, stick it on a cable, and plug it between the drive and the mobo PCIe slot.Then it's up to mobo makers to decide whether to just add PCIe x2 slots in the normal space (for use with either PCIe add-in cards or SATAe drives) or to add dedicated PCIe x2 slots over near the normal SATA slots for use with only SATAe drives.
SirKnobsworth - Thursday, March 13, 2014 - link
Why does it need to be attached with a cable? There are already PCIe form factor SSDs. If that takes up too much space then provide M.2 sockets on the motherboard. M.2 cards provide less area than 2.5" devices but that shouldn't be an issue for smaller SSDs, beyond which you really want more lanes anyway.