Adapter M.2 to 2.5"

[azrael]

Does anyone know and can recommend an adapter in the 2.5" form factor that can hold two M.2 drives, either NVMe or SATA, which can then be (converted to and) connected to SATA ports? PCIe would also work, but I wouldn't know how to connect them to the motherboard. I'm specifically not looking for PCIe cards that can hold M.2 drives,

 

[Sarajiel]

Does anyone know and can recommend an adapter in the 2.5" form factor that can hold two M.2 drives

I don't think those exist, since most adapters of that type try to stick to the 2.5" SATA drive spacing and only take a single M.2.
For example, SATA M.2 drives:
- RaidSonic Icy Box IB-M2S253
- Icy Dock EZConvert MB703M2P-B

For NVMe M.2 there exist similar, more expensive adapters for single drives as well:
- RaidSonic Icy Box IB-M2U04
- Icy Dock EZConvert MB705M2P-B
These NVMe adapters turn your M.2 drive basically into a U.2 one, that can be used with an HBA via an SFF-8639 connector.

I don't think there exist any adapters that convert NVMe M.2s into any form of SATA drive directly. Even the PCIe cards just change the connector types, not the protocol.
You might be able to connect a NVMe M.2 to an internal USB header by using an external M.2 enclosure and an adapter that turns the USB header into an internal port. However, you are stuck at abysmal speeds that way.

Alternatively, you could try one of those M.2 "hot-swap" solutions for 5.25" bays that usually take 2x or 4x M.2 drives. Not sure how reliable those are and if there are any that switch protocols, but that would be the option with the highest density of M.2 drives.
For example:
- Icy Dock ToughArmor MB720M2K-B (5.25")
- Icy Dock ToughArmor MB833M2K-B (3.5")
These use NVMe drives and need SFF-8643 connectors.