NVMe or AHCI PCI-express? A comment for people benchmarking...

A tangent to the performance testing thread here, but an important issue that you will see come up in your work this
yearor next.  

"PCIe SSD" may include AHCI PCI SSD or   NVMe PCI SSD.

AHCI = old style, basically it's faster than SATA3 but quite similar in terms of how the operating system sees the
flashdevice. 
NVMe = new style, requires a very new motherboard, operating system & drivers, but extremely fast and low latency, very
highIOPS.  
For example, Macbooks have PCIe SSDs in them, but not NVMe (currently).

The difference is very important since NVMe offers multiples of performance in terms of everything we love: lower
latency,higher IOPS, lower CPU overhead and higher throughput.  
http://www.anandtech.com/show/7843/testing-sata-express-with-asus/4
scroll down to the "App to SSD IO Read Latency" graph. Look at the two bottom lines.

So I'd suggest it's probably worth noting in any benchmark if you are using NVMe and if so which driver version, since
developmentis ongoing. 

On the topic of PCIe NVMe SSDs, some interesting reading:

- http://www.tweaktown.com/reviews/6773/samsung-xs1715-1-6tb-2-5-inch-nvme-pcie-enterprise-ssd-review/index.html
"it can deliver 750,000 random read IOPS and 115,000 write IOPS "

- or any of these nice toys...
http://imagescdn.tweaktown.com/content/6/7/6773_11777_samsung_xs1715_1_6tb_2_5_inch_nvme_pcie_enterprise_ssd_review.png

all with capacitor backing (which you should plug-pull test, of course).

Graeme.


> I currently have access to a matched pair of 20-core, 128GB RAM servers
> with SSD-PCI storage, for about 2 weeks before they go into production.
> Are there any performance tests people would like to see me run on
> these?  Otherwise, I'll just do some pgbench and DVDStore.