Hi, I have recently bought a 27" 5k iMac that has a couple of thunderbolt 3 ports. Since the fusion drive is like molasses when you are used to a MacBook Pro with a internal SSD I bought a 1TB external TB disk (https://eshop.macsales.com/item/OWC/TB3ENVPRC10) and installed macOS high Sierra 10.13.4 on it. I started to notice that after a time (hours) the drive would become very slow and cpu usage would be pegged at 100% even when the machine was idle. Also the GUI would update very slowly and the mouse would move unevenly. Also when in this state the machine would not power down/reboot properly but it would kernel panic at the end of the reboot/shutdown. I sent the drive back and OWC have tried to reproduce the problem but they have been unable to do so. The drive is on it's way back here now. The only difference I can think of is that I have parallels desktop 13 installed and I know it can present TB disks to VM's directly. This means that parallels have to insert itself in the thunderbolt dive stack and I suspect that it might be the cause of the problems. When I get the drive back I will try to remove parallels and see if the problem goes away. The reason for this post is to see if anyone else have seen behaviour like this when using a external TB drive (SSD in my case) and parallels. -Ivar
