Ursprünglicher Beitrag von: Dan ,
You have me scratching my head a bit here. Your system has a SATA III (6.0 Gb/s) interface so you should be able to gain the fully bandwidth of your SSD. By chance is your HD a SATA II (3.0 Gb/s) drive? If you can look I up, otherwise give us the make and model info. For now check your systems firmware level. Follow this Apple T/N: [https://support.apple.com/en-us/HT201518|About EFI and SMC firmware updates for Intel-based Mac computers].