Very slow write performance 30min+ for 2GB - APFS?
Okay after running
diskutil APFS defragment /dev/<yourdisklocation> status
I saw that defragment was disabled. Turning it on with
diskutil APFS defragment /dev/<yourdisklocation> enable
an waiting about an hour, the write speed startetd to return to "normal".
I could Copy the 2 GB in about 5 Minutes instead of 40´
Anyway - the Cruxial 500 MX 1TB SSD ist already in my Postbox.