Question Is U.2/U.3 the consumer's saviour from M.2?

[mikeymikec]

Tech_Junky started a recent thread about U.2 / U.3 which piqued my curiosity and so I've read up a little about it. Here's my understanding so far (feel free to correct me / supply more info):

M.2 without question has problems, most of which stem from a limited size area which also uses up a valuable amount of motherboard space. Its limited size in turn creates heat dissipation issues as discussed here:

Gen5 NVMe have active cooling

https://hothardware.com/news/consumer-pcie-gen-5-ssds-sale-in-japan A fan on an SSD? This is really getting quite ridiculous. These things are turning into GPUs.

forums.anandtech.com

My reading list so far:

What you can do with that U.2 port on your motherboard next to the SATA inputs | Poc Network // Tech

So you bought a new motherboard and you are getting ready to build your new system when you realize that there is this U.2 connection right by the SATA inputs. Now, if you are reading this, you likely don't know what that is and are wondering what on Earth you can do with it. U.2

www.pocnetwork.net

What you need to know about U.3 | Automated Testing Tools

What does U.3 mean for the ever-developing data storage industry? Here's a hardware engineer's perspective on this drive host controller

quarch.com

M.2 vs NVMe vs. 2.5" vs. U.2 SSDS

The types of SSDs include the 2.5”, the M.2, U.2 and NVMe PCIe SSD, each offering distinct advantages and disadvantages. Learn more here.

www.cdw.com

pocnetwork reports that U.2 can do up to 32,000MB/sec which seems like an obvious advantage to mention (M.2 gen 5 seems to be talking about 10k MB/sec - 15k). U.2 is hot-pluggable also.
pocnetwork also has a photo of a motherboard with a U.2 socket if anyone is interested in how that would look; it's similar in size to a couple of SATA ports by the looks of it.

Really though the main point for potential mainstream users is the idea that you can get your SSD away from other heat-generating devices like say a chunky graphics card or the processor; since SSDs will throttle bandwidth when they get hot enough and my (idle) M.2 SSD just by hitting near my (idle) graphics card will hit 50C (as opposed to about 37C without the graphics card, and even without a SSD heatsink). It also means that you can slap a chunky heatsink on the SSD and cool it with a large and near-silent fan if need be; basically a lot more flexibility for cooling solutions. U.2 also means that U.2 SSDs can be designed in a more spacious manner so they dissipate heat better since they're not longer limited by the size of the connector and the possible space allotted by the design of the motherboard.

One thing that concerns me with the U.2 / U.3 standard is that compatibility-wise it seems to be off to a messy start: U.2 drives are apparently not compatible with U.3 hosts but U.3 drives are compatible with U.2 hosts.

 

[Tech Junky]

The other benefit is price per TB.

8TB / M2 $800 and U is $400
16TB / M2 none and U $1000
30Tb / same outcome of M2 not existing.

Heat can still be an issue though for some brands as they're designed for use in a high static pressure environment with high airflow. My Kioxia drive idles around 40c though with no direct cooling.

 

[zir_blazer]

I find MUCH more interesing OCuLink, which like U.2 is intended for 4 PCIe Lanes, but the Ports and cables seems to be consistenly smaller and cheaper. Is also easy to make adapters between OCuLink and U.2 with a joint drive side connector in either Molex or SATA Power variants to support current U.2 drives on boards with OCuLink Ports.
I don't understand why there is no interest in doing a 2.5' drive with OCuLink input plus separate SATA Power. Mechanically it would pretty much look and behave exactly the same way than you would expect any SATA SSD but with a different connector. Sadly, OCuLink installed base being a zero on standard consumer systems doesn't help it.

 

[Tech Junky]

Sadly, OCuLink installed base being a zero on standard consumer systems doesn't help it.

Normal consumers don't know about the option. Besides the fact that it can be pricey until you hit 8tb in size. There is a power port on the drive side but it seems like a mini molex or pwm size. Connecting the SATA power to the cable seems easier for keeping things tidy.

In the end it's about reverse engineering things from the enterprise world at this point to save money on storage at nvme speeds.

 

[BFG10K]

They should've kept updating SATA like USB. SATA ports are cheap and easy to be plentiful on a mobo. 2.5" is a solved problem for heat, and you can put it anywhere in a case with double-sided tape, including next to 120mm/140mm intake fans .

The vast, vast majority of users don't need NVMe bandwidth for storage. For those rare people that do, the SSDs should sit in PCIe slots like graphics cards.

A 15W Voodoo 1 doesn't even need a heatsink, much less a fan / liquid cooling that these latest 10W PCIe 5 monstrosities need.

3dfx Voodoo Graphics 4 MB Specs

3dfx SST1, 50 MHz, 1 Pixel Shaders, 0 Vertex Shaders, 1 TMUs, 1 ROPs, 4 MB EDO, 50 MHz, 128 bit

www.techpowerup.com

 

[Igo69]

The other benefit is price per TB.

8TB / M2 $800 and U is $400
16TB / M2 none and U $1000
30Tb / same outcome of M2 not existing.

Heat can still be an issue though for some brands as they're designed for use in a high static pressure environment with high airflow. My Kioxia drive idles around 40c though with no direct cooling.

There were a 16 TB M2 but the price was absurd about $3K for 1

 

[Tech Junky]

There were a 16 TB M2 but the price was absurd about $3K for 1

Sounds about right.

 

[xyrium]

This is pretty good stuff. What are the drawbacks of these U.2/3 drives, limited read/writes as a tradeoff for raw speed? Perhaps random access is penalized in favor of streaming output?

Personally, I'm accustomed to paying far more per GB than what folks have paid in the past 10 years, going back to when 80MB drives were "big". So, I honestly don't believe many people would flinch at 8TB for only $400.

 

[Tech Junky]

drawbacks

Not many if you have a plan ahead of time. There's a mix of sides from mostly read, mostly write, or a balance. Heat can be an issue with some brands. Durability should be significantly better than their M2 counterparts. Speed is going to be about the same depending on the brand and purpose chosen. Can be slightly more expensive due to consumer boards needing an adapter and cable.

The plusses are the bigger than 8tb options if you don't feel like doing raid to get speed and capacity. They tend to run cooler due to having more surface area.

 

[thecoolnessrune]

Honestly there's just a lot of standards that fight each other that means investment is split into a bunch of initiatives. Laptops sell more than desktops, and M.2 there is almost mandatory in modern laptop designs. They aren't eager to hand back that valuable real estate to a 2.5" drive for no reason. Meanwhile, in the enterprise market, a move towards higher density means we're going to see most high end designs shift increasingly to EDSFF, which is made from the ground up for flash density. There is no parallel to this in the consumer market, and in all honesty I don't think it will ever get there. The design just isn't built for the meager needs of home users.

So that puts U.2 / U.3 / SAS-4 in this weird mid-market enterprise space for systems that need to flexibly design between 2.5" 3.5" disk form factors. This market isn't disappearing anytime soon, but it does mean that the home desktop user isn't really going to see the benefit of any of these designs. I personally loved the idea of SATA Express where one could choose either a SATA port, or x2 PCIe lanes to the end of the device. The outcome is equivalent to modern Tri-Mode SAS-4/SATA3/NVMe controllers, and in fact you could say they carried the torch, just in a much more expensive, higher capability device. It's too bad SATA Express hasn't continued to be iterated on, but at the same time PCIe 4 and 5 specs are so tight that engineering a commodity cable likely would have ruined the cost effectiveness of SATA Express in the first place. Consumers largely aren't going to pay $60 for a cable.

Ultimately high end consumers will continue having the option of acquiring these U.3 NVMe drives and using a PCIe adapter, but I think M.2 is here to stay in the consumer space by sheer force of volume sales.

 

[Hail The Brain Slug]

pocnetwork reports that U.2 can do up to 32,000MB/sec which seems like an obvious advantage to mention (M.2 gen 5 seems to be talking about 10k MB/sec - 15k).

This doesnt make any sense. U.2 carries the same x4 PCI-e link that M.2 does. It is not faster.

 

[Tech Junky]

This doesnt make any sense. U.2 carries the same x4 PCI-e link that M.2 does. It is not faster.

If you mux 4 drives through bifurcation it's possible.

Gen 4 @ 8GB/s * 4

Mind you there's no real daily use case for that kind of speed in the consumer realm. The only time you max things out is with a speed test. Real data doesn't move that fast in real life. Even copying data between 2 M2 drives on my laptop usually tops out under 2GB/s but TB 4 hits 3.1GB/s because it uses a different path. Maybe a full sized PC setup will hit higher? I haven't tested it but I do have gen 4 drives between the M2 and U3. They both hit Linux drive speeds over 6GB/s.... I also have a second M2 that I rsync to as a backup. I usually just test them before putting data on and then leave them alone as it doesn't really matter as long as the drives are working and not spitting errors.

 

[Hail The Brain Slug]

If you mux 4 drives through bifurcation it's possible.

Gen 4 @ 8GB/s * 4

Mind you there's no real daily use case for that kind of speed in the consumer realm. The only time you max things out is with a speed test. Real data doesn't move that fast in real life. Even copying data between 2 M2 drives on my laptop usually tops out under 2GB/s but TB 4 hits 3.1GB/s because it uses a different path. Maybe a full sized PC setup will hit higher? I haven't tested it but I do have gen 4 drives between the M2 and U3. They both hit Linux drive speeds over 6GB/s.... I also have a second M2 that I rsync to as a backup. I usually just test them before putting data on and then leave them alone as it doesn't really matter as long as the drives are working and not spitting errors.

And you could do the same with M.2. It doesn't have anything to do with U.2.

 

[Tech Junky]

This doesnt make any sense. U.2 carries the same x4 PCI-e link that M.2 does. It is not faster.

And you could do the same with M.2. It doesn't have anything to do with U.2.

Ok, let me put this another way then.

The adapters you can opt to use are not locked to a certain speed like an M2. You're only bound to the speed of the slot or socket you insert them into plus the speed of the drive.

If you use a Gen 5 slot the max speed at x16 could be higher than x4. If a drive that exists with x16 bandwidth were used then you would get your 32GB/s.

U.2 can do up to 32,000MB/sec which seems like an obvious advantage to mention

The way this is read is the physical and electrical capabilities of the connector itself are capable of 32GB/s when spread across more than x4.

The problem right now would be no drive exists yet to aggregate that much band width into a single connection. A couple of reasons come to mind... Heat / price / density. If a drive hitting those speeds did exist it would probably be a slot based implementation like the aic options built onto the PCB with fans.

However there are x4*4 adapter PCB options that can hold four drives on a single card for about $80.

 

[DrMrLordX]

Adapters are going to make U.2/U.3 a non-starter for consumer platforms. If U.x is going to make it on desktop, there needs to be native board support.

 

[Shmee]

Adapters are going to make U.2/U.3 a non-starter for consumer platforms. If U.x is going to make it on desktop, there needs to be native board support.

I recall a fair amount of HEDT boards, particularly for X99 I think, had u.2 ports on them. Of course HEDT is much more $$$$ now unfortunately, and is less gaming/consumer/DIY oriented in general.

 

[xyrium]

Adapters are going to make U.2/U.3 a non-starter for consumer platforms. If U.x is going to make it on desktop, there needs to be native board support.

Possibly. It may simply become an enthusiast entry into the enterprise market. I don't believe any of the current drive mfrs are concerned about consumers adopting the format for personal use.

 

[AdamK47]

I'm thinking of switching to U.2 when I replace my three 8TB PCI-E 3.0 m.2 RAID-0 drives. A single 32TB drive will work. m.2 has been stuck at 8TB for far too long.

 

[DrMrLordX]

Possibly. It may simply become an enthusiast entry into the enterprise market. I don't believe any of the current drive mfrs are concerned about consumers adopting the format for personal use.

They should be, given the stupid heatsinks that are necessary for some PCIe 5.0 drives.