Answer to: I think I have lost my fusion driveWhere exactly did you delete the contents? (Disk Utility in the installer?) We really need to see output from diskutil list and diskutil cs list in Terminal, but it looks like you might have partitioned the drives again while erasing. In this case the system will be slower because the OS is running from the platter HD, not the SSD. What you need to do is start Recovery Mode, go into Terminal under the Utilities menu and run a few commands to recreate the Fusion drive. (Many DIY instructions on the net) After that is complete you can restore using Time Machine.