M.2, U.2, NVMe, 2.5" SSD...Huh??

OK, I admit it, I bought this without fully researching it but I think I understand what it is supposed to do, maybe, I think, or maybe I do not have a clue, which is more likely than anything else.

Anyways, I bought an ASRock U.2 kit which came with just a Add On Card that says M.2 to U.2 Add On Card. It was cheap, like $18 or so.

So I think that this card fits in one of the two NVMe drive slots that I have on either my X370 Taichi or my X470 Taichi Ultimate motherboards. What I think that it is supposed to do is to connect a 2.5" SSD SATA III connected drive to the NVMe slot instead of the SATA III port on the motherboard thus increasing the data though put/flow rate to near NVMe M.2 standards IF the slot on the motherboard supports this. Now the two slots on the ASRock motherboards that I have list one slot as 1 Ultra M.2 (PCIe Gen3.0x4), and the other slot as 1 M.2 (PCIe Gen2.0x4). Now PCIe is supposed to be super faster than SATA III for data transfer rates and basically this card is to allow a 2.5" SSD to plug into the NVMe slot so that the SSD will now act like a M.2 drive under the NVMe standards (PCIe) vs the SATA III standards.

Is this correct?

So basically this is a poor mans work around to utilize NVMe 3,500 MB/s (3.5GB/s) standards with a 2.5" SSD instead of the SATA III standards of 600MB/s. Of course, this also depends on the 2.5" SSD capabilities and also whether the motherboard NVME slot used for the add in card is either PCIe 3.0X4 or PCIe 2.0X4, the 2.0X4 being slower than the 3.0X4 NVMe slot, right???? being the 3.0X4 (3.0 standard with 4 PCIe channels at 32GB/s) vs the (2.0 standard with 4 PCIe channels at 20GB/s)?

So if I buy a cable that goes from my 2.5" SSD that is currently plugged into a SATA III port and instead connect to the U.2 Add On Card port, and plug said 2.5" SSD into one of the NVMe slots using the Add On Card, in theory I should start to get a much faster data transfer rate from the 2.5" SSD because it is now acting more like a NVMe drive using either the 3.0X4 or 2.0X4 NVMe data rates instead of the SATA III, PROVIDED that the 2.5" SSD can support that data transfer rate, right? At 32GB/s for the Ultra NVMe slot and 20GB/s for the "older" NVME slot using the 2.0X4 standards.

So having multiple 2.5" SSD SATA III and using one of them (the fastest data transfer one, ie the fastest Read/Write data transfer) in the above fashion would then give me the "poor mans NVMe drive" if I understand this correctly.

I know that there is a lot of confusion on my part with the standards (3.0 and 2.0) and the data streams X4 PCIe vs SATA III. Hey, I am a carpenter by trade not a computer engineer.

So from a layman's point of view is this kinda right?

xhue wrote: Bwoy, oh, bwoy! Where do I start here? SATA is a bus interface, i.e. some pins in some connector with a given shape. Max current speed of 6Gbps. AHCI is the most largely spread protocol for communication with disks over SATA. M.2 is again a bus interface. It utlizes only NVMe for now. Max 32Gbps (PCIe v3 x4 lanes). U.2 is a bus interface too. Onlt that it's designed for enterprise and industrial use. There is a certain confusion because some M.2 SSD could use SATA/AHCI. BUT (!) you won't be able to use a SATA SSD in U.2 slot. Even if you somehow do so, the SSD will again run @ 6Gbps because of its internal controller.

So PCIe, SATA II, SATA III, NVMe, and U.2 are interfaces, ie, just port interfaces to connect certain items via cables and slot connections to motherboards. Do IDE ports/FFD ports (using the ribbon cables) also fall into this category? What about PCI and AGP? Bus interfaces or protocols? or both? PEX?

And then there are communications protocols like AHCI (there is an older legacy one also right?), 3.0X4 and 2.0X4 (for NVMe drives).

Is this because the Industrial and Enterprise do not use SATA III bus connections but use NVMe bus connections only for drives? Does this include internal LapTop drives falling into this category?

Or is it that the 2.5" SSD is an entirely different SSD than the Enterprise/Industrial SSD's and they just happen to look pretty much the same....except for the power/data hook up, identical looking SSD's (same type of memory chips?) but two entirely different interfaces and controllers, one SATA III 6GB/s the other U.2 to M.2 2.0X4 or 3.0X4.

So in essence a 2.5" SSD SATA III architecture is NOT COMPATIBLE with the U.2 NVMe architecture due to the disk on board controllers and power/data connectors and there is NO WAY to use a SATA III 2.5" SSD with a U.2 to NVMe interface or protocol.

I found this and it explained it a little better for me to understand. I hope I am not violating rules by posting an article excerpt that pretty much explains what I have been trying to figure out.


U.2 and NVMe - To speed up the PC performance

An important factor for PC performance is the hard disk or SSD that is implemented. Then again, what matters here are two things: the interface technology and the data transfer protocol. In the following the interface U.2 and the data transfer protocol NVMe will be explained in more detail.

After that it will be shown how far U.2 and NVMe play a role for the SSD or, to say it in general words, in which ways these technologies influence the operating speed of the PC.

The U.2 interface

The technologies in detail

1. The U.2 interface

U.2 is applied for NVMe SSDs in 2,5" format. Initially, this interface was labeled as SFF-8639. In 2015 the SSD Form Factor Working Group (SFFWG) decided on the simpler name U.2 that also goes well with the established M.2 interface.

In the area of workplace PCs the U.2 interface is not even widely used at present. For conversion there are M.2 to U.2 adapters or PCIe to U.2 plug-in cards available. The converters have a SFF-8643 socket; for connection a suitable U.2 cable with SFF-8639 or SFF-8643 plug has to be used. In contrast to SATA Express, the U.2 interface makes use of additional pins that support the transport of four PCIe lanes.

2. The NVMe protocol

NVM Express ( = NVMe) is a more sophisticated data transfer protocol for the PCIe bus and successor of AHCI (Advanced Host Controller Interface) that was published in 2011 for the first time. NVMe stands for Non-Volatile Memory Express, which means a protocol for persistent storage media. It isn't limited to SSDs but is designed for persistent memory in general.

When NVMe was developed the focus was an optimized command management (submission und completion). Because of the high speed of PCIe SSDs it was also paid attention that as much as possible commands can be processed parallel. Thanks to the more efficient way to distribute commands, the latency (time delay) is significantly reduced. As a result, the sequential read and write performance of data is improved.

To say it simple: the faster the "waiting" CPU can receive data, the sooner these data can be passed on, which means: the faster the PC is working.

In which ways do U.2 and NVMe influence the PC performance?

HDD versus SSD

The working speed of a PC is considerably defined by the storage media on which system software and programs are installed. These days, customary hard disc drives (HDDs) are being replaced by SSDs more and more. SSD stands for Solid State Drive resp. Disc. SSDs have no longer movable mechanical components like HDDs, for example read head or magnetic disc.

Storage processes at SSDs run purely electronical. There are no longer easily damageable engine suspension and read-write-mechanics at SSDs which makes these much more robust and shock-resistant, so SSDs are suitable for mobile applications in particular. Further advantages are very short access times, silent operation, low weight, low power consumption and few waste heat. That's especially important for notebooks and other mobile devices and supports also a long battery life.
SSD and U.2 / NVMe

Classic hard discs, already limited in their memory speed by the mechanical structure, are still using the SATA connector and the AHCI data transfer protocol. As said above, SSDs in itself are considerably faster than HDDs, indeed. But now the used interface technology and data transfer protocol can act as speed brake furthermore. Practically said: SSDs via SAS or SATA that use the AHCI protocol do not reach the speed optimum.

Via SATA connected SSDs with AHCI have data transfer rates up to maximal 0.6 GB/s. SSDs with PCIe-3.0 connector and AHCI get to speeds of about 1 GB/s, once they use one transmission channel ( = 1 lane).

Let's suppose the use of four lanes, the speed would theoretically quadruple and get to 4 GB/s. Practically, that's now made possible by the use of PCIe SSDs which work with the NVMe protocol, whereby the current speed optimum is reached.

DATA TRANSFER RATES BY COMPARISON

Memory      Speed
HDD      ~ 0,1 GB/s
SSD (AHCI) with SATA connector      ~ 0,5 - 0,6 GB/s
SSD (AHCI) with PCIe connector      ~ 1 GB/s (1 lane)
SSD (NVMe) with PCI connector      ~ 4 GB/s (4 lanes)

Finally, in case a NVMe SSD in 2.5" format shall be applied instead of a plug-in card that can be plugged directly into the M.2 or PCIe slot, the U.2 interface comes into play. In place of the direct way, the PCIe bus can be connected via a U.2 cable. So the support of four PCIe lanes is ensured again.



Think I am going to buy a U.2 drive just to experiment with it. Guess it will not be much longer that the SATA II/III HDD and SATA III SSD's become legacy items. Does anyone make a motherboard that only has NVMe busses?

And all this will become useless when we finally get into crystal storage with transfer rates that are comparable to the speed of light, providing the supporting hardware supports such a high data transfer rate structure. Wonder if I will ever see 6 TGB/ns (6 trillion giga bytes per nano second) or 6 trillion billion bytes per 10^-9 seconds. In layman terms, you would get there before you even left. Did not the CERN facility in Switzerland/Italy accelerate a particle to FTTSOL a couple of years ago?