High Sierra doesn’t recognise an SSD

I installed High Sierra on an external Samsung 850 Evo SSD as my startup disk. This is inside an Inateck FE2010 case, so is fast and reliable. But not only will it not convert to APFS format, the Info tab in Disk Utility says it’s not a solid-state drive. What’s wrong? There’s almost certainly nothing wrong with your SSD or its case. This is a bug in High Sierra 10.13. The 10.13.1 update fixed several bugs in APFS and Disk Utility, so the first thing to do is update to the latest version of macOS available (10.13.3 at time of writing), and you might find it now correctly identifies the SSD and can format it in APFS.

Download the current High Sierra installer from the Mac App Store and start again, formatting the drive from scratch and installing a fresh copy of macOS on it. The simplest way to do this might be by making a bootable installer on a USB memory stick.

If you still encounter any problems with your SSD after this, contact Apple support ( support.apple.com) and report them, because the issues will need to be fixed.

One important caution for anyone running High Sierra from an external drive is not to try to create a “dual-boot” system, in which you switch back to running Sierra on the internal drive. We’ve seen reports of serious problems restarting in Sierra after running High Sierra from another volume — Time Machine backups being damaged and forcing a complete backup to be made, and Sierra suffering repeated disk errors with any connected APFS drive.

Upgrading an SSD startup disk to APFS is a one-way process, and getting back to Sierra, even for short visits, can be tricky.