Synology's DSM exposes disk health, volume usage and system status over SNMP once it's turned on in Control Panel.
In DSM, go to Control Panel > Terminal & SNMP > SNMP and check Enable SNMP service; it's off by default.
SNMPv2 with a non-default community string is the common baseline; SNMPv3 is available for encrypted polling if your DSM version supports it.
Synology's MIB reports per-volume usage, disk temperature and SMART status, RAID state, and system fan speed, giving you the same failing-disk-before-it-fails visibility you'd want from any storage array.