Synology DS1821+ Hardware Installation Manual page 6

Transitions between System Modes
To better understand the transition between system modes, please refer to below examples:
• Powered on with no DSM installed:
Powered off > Powering on > DSM not ready
• Powered on with DSM installed:
Powered off > Powering on > DSM not ready > DSM is ready for use
• Enter hibernation then wake up from hibernation:
DSM is ready for use > Hibernation > DSM is ready for use
• Shutdown Synology NAS:
DSM is ready for use > Shutting down > Powered off
• Power failure with UPS attached:
DSM is ready for use > DSM not ready (due to power failure, DSM enters safe mode) > Shutting down >
Powered off > Powering on (power has recovered, DSM will reboot)> DSM not ready > DSM is ready for use
6 Chapter 1: Before You Start