Looking for advice on NVMe (U.2) adapters

[ghxst]

I'm looking for some advice on reliable solutions for connecting two U.2 NVMe drives (one of which is an Optane 905p) to a PCIe Gen 5.0 slot running at x8. My goal is to minimize latency, but I am not sure if that's a concern at all with these cards. A friend of mine had a similar setup but encountered issues with cables and adapters, which affected his performance on the Optane drive quite negatively. He eventually found a working solution, though it felt more like luck than strategy so I figured I'd try my chances asking for some advice here.

I’d like to just be aware of any pitfalls and avoid them when I'm looking around on eBay or AliExpress to see if I can find anything that can make this setup work. If anyone has experience with low-latency, stable U.2 to PCIe adapters, I’d greatly appreciate any recommendations.

Additionally I will need to pick up 2 or so HDDs for long term storage and SAS might be a cool solution if I could fit them on the same card since I wouldn't mind sharing the bandwidth of those with the second drive, if that's at all possible.

 

[Tech Junky]

I use oculink for my drive. Picked up a single M2+cable for it on Amazon for ~$40 and get 6.5GB/s out of it.

There are some cards though that have dual oculink ports in them for about $50 and give you 4 drives total. Could get a dual U cable and a dual SAS cable.

 

[ghxst]

I use oculink for my drive. Picked up a single M2+cable for it on Amazon for ~$40 and get 6.5GB/s out of it.

There are some cards though that have dual oculink ports in them for about $50 and give you 4 drives total. Could get a dual U cable and a dual SAS cable.

Oh interesting! There's no added latency with the oculink? I was originally more thinking about a PCIe card specifically for drives but going with a card that has oculink connectors would make it useful for other stuff too. Will definitely investigate that option further.

 

[Tech Junky]

no added latency

I haven't observed any issues with it. I'm not really focused on latency though but, testing the drive and getting the speeds on the sticker is good enough for me.

Of course the big caveat is going to be if your MOBO does bifurcation or not. If it doesn't then the PCIE option won't work as the system will only pick up a single drive.

 

[nexox]

The only possible component in this kind of setup that adds latency by design is a PCIe switch, which you need if your system doesn't support bifurcation. Cables and connectors don't add latency, and retimers add a negligible amount of latency, but if they don't achieve sufficient signal integrity they can require data to be re-transmitted, which does take a long time and thus increases latency substantially. As far as finding the combination of cables and adapter that work for you, there may be some experimentation, though with PCIe 3.0 SSDs like the 905p there should be fewer signal quality issues.

SAS on the same card means a Tri-Mode controller, which generally ruin the performance and protocol features of NVMe drives, no point connecting Optane to that, you would be better off just going all SAS NAND SSDs and a cheaper HBA that doesn't support NVMe at all.

 

[Sean Ho]

How are you planning on mounting these U.2 drives? Do you have an NVMe backplane, and if so is it tri-mode or U.3? Or 2x2.5" bays but direct-cabled, without a backplane? Or are you thinking of a cheap PCIe x4x4 card with 2x U.2 directly on the card, relying on motherboard bifurcation?