Why is my SSD booting from USB and not from SATA
I installed OSX 10.10.4 on a Samsung 840 EVO using an external SATA - USB enclosure.
When restarted, my MBP booted from the SSD but when I installed the SSD in the HDD SATA bay all I got was a map picture with a question mark in it. The SSD was not recognised.
Then I put the HDD in the external enclosure and restarted. The MBP booted from the HDD and in Finder the SSD was present and could be explored.
In system preferences the SSD was marked as boot drive.
The SATA bus is 6 Gb, the cable is OK (working fine with the HDD) and I installed the latest firmware for the SSD.
Any ideas what can be wrong ?