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I answer this myself.
In "Intel Rapid Storage Technology" the disk is reported as "Offline" and there is an option to "Clear and reset disk". I haven't dared to do the clear and reset because I'm unsure if it means that all data on the disk will be lost.
Instead I made an Ubuntu USB pin and booted the computer from it. Now, from Ubuntu I can see all my files on the old drive and also copy them to my new drive.
Please note that you must cancel any acceleration of the new drive before copy the files to it or else it won't work.
Hope this helps someone.