Thanks Neil, Excuse my delay in responding. I am on the digest. I incorrectly stated that I wanted to separate the OS from the applications. What I meant to say was to separate the work data from the OS and application. Therefore move that data to the second internal SSD. Equally back-up each of them to a separate external drive, with the third external being used as a Time Machine backup. The machine is not a server but my work station. I would therefore appreciate advice on a different allocation of drives and specific applications. Take care, Roy