You can also use thunderbolt powered external hard drives

My Passport Pro Portable External Hard Drive - Thunderbolt - WDBRMP0020DBK-NESN

I have an expensive portable Western Digital RAID drive (see it at WD 2TB

We can use our old machines or our newest machines with our ultra-fast Thunderbolt portable drives.

I connected it to my Thunderbolt 2 iMac (5k version) to a Thunderbolt 3 hard drive (USB-C) and it is not compatible!!

I had also read that some reviewer had successfully connected an external hard drive to their MacBook Pro (an earlier model than mine) with this device

I have an expensive portable Western Digital RAID drive (see it at WD 2TB

My Passport Pro Portable External Hard Drive - Thunderbolt - WDBRMP0020DBK-NESN

This works for my hard drive connections.

Works like a charm both for connecting my old 27" Thunderbolt monitor as well as for Lacie 2TB rugged external thunderbolt hard drive

It is well-built, and I've had no trouble with it on multiple Thunderbolt 2 drives I have been using

If you use it and buy an external hard drive that does not have it's own power source, the device will not work.

I had purchased aPrime 2TB USB-C to Micro-B External Portable Hard Disk Drive Build in WD Blue Inside for new MacBook 12" Retina, MacBook Pro with Touch Bar, iMac Pro (2TB) to get that extra storage I needed along with a backup option