With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
ciscoFlashPartitionSizeExtended
cisco Flash Partition Size Extended
1.3.6.1.4.1.9.9.10.1.1.4.1.1.13
Flash partition size. It should be an integral multiple of ciscoFlashDeviceMinPartitionSize. If there is a single partition, this size will be equal to ciscoFlashDeviceSize. This object is a 64-bit version of ciscoFlashPartitionSize
Back to CISCO-FLASH-MIB MIB page.
IPHost Network monitor allows you to monitor ciscoFlashPartitionSizeExtended on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco routers right now.