SNMP Poll Reports Different Memory Usage than show system resources""

Symptom

The value reported by snmp poll for hrStorage (hrStorageRAM) shows very different value than memory use reported by the show system resource command.

Values from SNMP poll:

HOST-RESOURCES-MIB::hrStorageIndex.1020 = INTEGER: 1020

HOST-RESOURCES-MIB::hrStorageType.1020 = OID: HOST-RESOURCES-TYPES::hrStorageRam

HOST-RESOURCES-MIB::hrStorageDescr.1020 = STRING: Slot-1 Management Memory

HOST-RESOURCES-MIB::hrStorageAllocationUnits.1020 = INTEGER: 1024 Bytes

HOST-RESOURCES-MIB::hrStorageSize.1020 = INTEGER: 4057060

HOST-RESOURCES-MIB::hrStorageUsed.1020 = INTEGER: 866824

Values from show system resources:

> show system resources

top - 15:26:01 up 19 days,  3:16,  3 users,  load average: 0.40, 0.45, 0.21

Tasks: 111 total,   1 running, 110 sleeping,   0 stopped,   0 zombie

Cpu(s):  4.2%us, 11.4%sy,  0.6%ni, 83.3%id,  0.0%wa,  0.0%hi,  0.5%si,  0.0%st

Mem:   4057060k total,  3894776k used,   162284k free,  279116k buffers

Swap:  2008084k total,        0k used,  2008084k free,  2748044k cached

Cause

The value reported via SNMP takes into account that Linux-based systems use buffers and cache in memory to speed up disk operations. These buffers are freed when memory needs to be used/allocated. Once this is taken into account then 3894776-(279116+2748044) = 867616, which is very close to the value received from the SNMP poll.

owner: rweglarz