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I'm contemplating the use of U.3 drives in my next desktop PC build, although I have no direct experience with them. (The reason for considering them is largely because I want to be able to run at least some of them in RAID 1 and rotate the drives out periodically; having hot-swap capability would also be nice. Given that M.2 drives are generally right on the motherboard, swapping them out is much less convenient. My current build uses SATA drives but they are now unacceptably slow, relative to the NVMe competition.)

I have found some U.3 enclosures for between 2 and 6 drives (also some U.2, and indeed some say they can do both). These are typically 5.25 inch units with front-opening ports for inserting/removing drives.

The cabling also seems to be straightforward, though I confess I've slightly glossed over that part so far.

However, connecting the drives to the motherboard is less obvious, as I can't find U.3 host adapters. I strongly suspect I'm missing the point somewhere, so this is the main point on which I'd really appreciate some guidance...

I have found multiple different PCIe x16 cards which have 4 SFF-8643 connections, but all of these say they are for U.2 drives. Since I have read that U.3 drives can be used in U.2 backplanes (but not vice-versa), perhaps such cards would actually be an acceptable way to proceed? (Perhaps they are the only way to proceed in fact?!) I've yet to find a single U.3 PCIe card, which baffles me.

I'll note that I've also found adapters which allow an M.2 drive to be converted to U.3 (or U.2) form factor. I would certainly consider using these as part of my setup (it seems to be slightly easier/cheaper to buy M.2 drives than U.3 in the <= 4 TB range), since with a multi-drive enclosure I'd still get the benefits of easily swapping out drives, and I'd just need as many adapters as M.2 drives to keep things really simple. (I don't yet know if this would permit hot-swapping.)

(Regarding the actual enclosures, cables, PCIe cards (etc.) that I've found, I'm not sure it's OK to insert links to commercial offerings here so I'll not do that right now, but happy to add some if this is permitted.)

PS: I have also found PCIe cards onto which a single U.3 drive can be mounted, but I don't see much benefit in these for my application. PPS: this is my first question on this part of the network, and I'm hoping this is the right place to ask it...

Neilski
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  • Not that U.3/U.2 isn't great, but what about using one of IcyDock's various hot-swap M.2 products instead? I think it might fit your use case a little better while taking less space/money. – JMY1000 Dec 16 '23 at 21:56
  • @JMY1000 Thanks (and sorry for slow reply). Yes, I'd certainly consider these, or indeed their similar U.2/3 enclosures - they were actually among the products I was talking about in my question. The issue had been that I couldn't find adapters to connect pretty much any of them to my PC at "sensible" costs, from recognisable vendors. If you know of cost-effective ways to connect those Icy Dock products to a PC I'd be grateful for pointers. Maybe I should contact Icy Dock for their current recommendations (given that their list seems outdated, with many listed items no longer available). – Neilski Dec 26 '23 at 13:43
  • @JMY1000 PS: I've read in a few places that M.2 remains non-hot-swappable even when used in enclosures like these. The Icy Dock product page seems to imply that it might work though. Not a showstopper for me of course. – Neilski Dec 26 '23 at 13:44
  • Yeah it might be worth contacting IcyDock. Their PCI-e to 2x hot-swap-bay cards don't require any additional cabling or PCI-e cards, but it's relatively low density. My understanding is that M.2 hot-swap should work, but that motherboard vendor support for PCI-e hot-swap tends to be kind of poor in general. – JMY1000 Dec 27 '23 at 01:54
  • @JMY1000 - will give them a try, thanks – Neilski Dec 27 '23 at 23:14

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I have also searched and I was not surprised to land at microsatacables -- in all things SFF/PCIe and similar they are a well known and reliable vendor. They have a PCIe Gen 4 OCulink (SFF-8611) to U.3 (SFF-8639) Cable and a U.3 Female (SFF-8639) to Mini SAS HD (SFF-8643) cable.

You can read more on U.3 here which mentions

A U.3 NVMe drive is backward compatible to U.2 drive bays

so presumedly any U.2 cable would work too. We can create a single U.2 drive bay with a U.2 SFF-8639 NVMe SSD to PCI-e 4X Adapter. This is also available in cable format from adt-link, a well known company for PCIe risers: PCI express 4.0 x4 to U.2 (SFF-8639) Extension Cable.

This forum post confirms

the CBL-SAST-0956 cable works with my Micron 7450 Max U.3.

The CBL-SAST-0956 is an OCULink - U.2 cable.

So no matter how you get four PCIe lanes off the motherboard, be it a PCIe 4.0 x4 slot, an U.2 connector or an OCUlink connector there is a cable for it -- just get the U.2 cable if nothing else is available.

chx
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  • Many thanks for reinforcing the point that U.3 drives should work just fine with a U.2 interface (and sorry for slow reply here too). I'm still battling the question of how to get the PCIe lanes off the motherboard though, whether as Oculink, SFF-nnnn or other. My dream product would be a PCIe 4.0+ 16-lane 4-port card from a reputable vendor - I would likely then hook this up to a 4-bay dock. Have you come across any such products in the few-hundred-£ price range? – Neilski Dec 26 '23 at 13:44
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    That's a separate question and depends whether your motherboard "BIOS" supports bifurcation. If it does then the IOI QIP4X-PCIE16XB03 sold retail as Delock 90111 would be an obvious choice -- IOI is gold standard in this space (whether the Aubess PH49 is a cheap knockoff or the same is anyone's guess). If it does not, well, ask separately for a quad M.2/U.2/OCuLink card without bifurcation requirement. That's a challenge. And it'll be over a thousand dollars. Look here https://www.serialcables.com/product-category/gen4-broadcom-host-cards/ for some examples. – chx Dec 27 '23 at 11:48
  • thanks again for the pointers! – Neilski Dec 27 '23 at 23:15