Connecting an external SSD
How can I connect a Thunderbolt 3 Q external SSD to my iMac 27-inch Late 2015 with Thunderbolt 2 ports, so that when I upgrade my Mac
I can continue using it?
The simple answer might appear A to be connecting it using Apple’s Thunderbolt 3 to 2 adaptor, but alas that usually doesn’t work as it can’t deliver the power that a compact external SSD normally needs. Equally, buying a Thunderbolt 1 or 2 compact SSD would suffer the same problem when you came to connect it to a current or future Mac.
In light of these issues, you can either buy a more expensive powered external SSD or enclosure, or a dock to provide the power that a compact unit needs. If you get a
Thunderbolt 2 dock now, you should still be able to use it via an adaptor when your Mac has Thunderbolt 3 ports. Another option would be to mount an M.2 NVMe SSD in a compact Thunderbolt 2 case for the moment, and then replace that with a Thunderbolt 3 enclosure when you upgrade your Mac. A second factor to consider is that compact SSDs initially claiming better performance than cheaper SATA models will eventually slow down when they have to cope with sustained writes. This is because they rely on passive cooling in operation, which can’t keep them cool enough to write at full speed for too long.
To realise the full potential of a fast M.2 SSD, it has to be mounted in an enclosure with active cooling such as a fan, which is how Apple’s internal SSDs invariably perform better than compact external SSDs.