In the new macOS High Sierra, Apple has introduced a new file system called Apple File System (APFS). When users upgrade, their filesystem is automatically converted to APFS from the standard HFS+ format, with no option for opting out of the conversion.
Filesystems are complicated beasts. macOS has been running on HFS+ since 1998, for good reason. It is a tried and tested, stable filesystem that has powered every single Mac computer to date. Forcing a brand new file system on every user upgrading to High Sierra is a daunting task, and people are already experiencing tons of problems such as the upgrade failing, files being deleted, pro apps not working properly, etc.
APFS is a great upgrade. It brings tons of improved performance and is optimised for Solid State Drives. But it is arguable far from perfect, and even introduces simple, devastating bugs such as exposing encryption keys that would leave any Apple developer dumbstruck.
The latest issue with APFS comes in the form of introducing an extra 15 seconds of booting time when Trim is enabled. It is currently believed that the filesystem is performing a routine Trim-related cleanup process during this time, which is causing boot times to increase for users who want their SSD’s to benefit from Trim.
Enabling Trim with Trim Enabler or Disk Sensei still works fine in High Sierra and will not introduce any other issues. It is still required to enable Trim to get the feature on third-party SSD’s in High Sierra. Trim is an important feature for Solid State Drive performance and longevity. Some users who want to enable Trim on High Sierra may notice an increase in boot time for now. I have opened a discussion with Apple developers about fixing the boot time issue in APFS. I am convinced this is an unintentional bug in APFS from Apple’s side that should be fixed in an upcoming version of High Sierra.