Since DSM does not allow downgrading if you choose to preserve settings, you need to trick it to believe the installed version is older version   Assumption: You have updated to newer version 6.2.2 (DSM_DS3615xs_24922.pat) and it is bricked You want to rollback to 6.2 (DSM_DS3615xs_23739.pat) with setting preserved   Prerequisite Your original USB boot key (For 3615) (USB Drive A) Any Live Linux USB key (e.g. Debian)  (USB Drive B) An additional USB b