The Routing Engine boots from the storage media in this order: the USB device (if present), then the internal flash disk, then the hard disk, then the LAN.
If the Routing Engines are configured for graceful switchover, the backup Routing Engine automatically synchronizes its configuration and state with the master Routing Engine. Any update to the master Routing Engine state is replicated on the backup Routing Engine. If the backup Routing Engine assumes mastership, packet forwarding continues through the services gateway without interruption. For more information about graceful switchover, see the JUNOS System Basics Configuration Guide.
Note: For specific information about Routing Engine components (for example, the amount of DRAM), issue the show chassis routing-engine command.