Odd values for various memory metrics via SNMP

Hi all,

what's the best platform/list/forum/... to discuss issues with the SNMP implementations
for FreeBSD? Since I started to dig deeper into Obervium I found that of all the systems
I own only the FreeBSD based ones present some challenges regarding the interpretation
of memory metrics.

1. I confirmed that this is not an Observium artefact. LibreNMS and manual snmpwalk
give the same results.

2. This is independent of the question if you use net-snmp (FreeNAS, OPNsense) or
bsnmpd in base (my Raspberry Pi cluster).

3. These are the systems concerned:

- OPNsense - FreeBSD 13.2, AMD64, 8 G of RAM, net-snmp
- FreeNAS - TrueANS CORE, FreeBSD 13.1, AMD64, 64 G of RAM, net-snmp
- 7 Raspberry Pi CM 3+, AARCH64, 1 G of RAM, bsnmpd

4. The "odd" metrics:

- "Real Memory"

OPNsense: 762 of 768 M (yes!) used, flagged "red" in Observium, of course
FreeNAS: 35.9 of 36.1 G used
All the Pis: 178 of 179 M used

All - see hardware description above - no connection to the "real real" memory installed.

For comparison: ESXi 8.0: 26.7 of 31.9 G used - the system has got 32 G of RAM installed.

- "Shared real memory"

OPNsense: 97.1 of 103 M used
FreeNAS: 593 of 774 M used
Pis: 11.8 of 12.4 M used

- Shared virtual memory

Only systems running net-snmp have this, bsnmpd based ones don't.

OPNsense: 166 of 233 M used
FreeNAS: 1028.27 M of 1.49 G used

- Virtual Memory

Again, only via net-snmp.

OPNsense: 5.03 of 5.11 G used
FreeNAS: 628 of 628 G used - that's particularly weird for a system with 64 G of RAM
	installed and not swapping or anything.

For comparison: my only Linux based system: 12.7 of 29.6 G used - the system has
	16 G of RAM plus 16 G of swap, that seems to match the "29.6".


For me these numbers don't make any sense at all. The motivation to write this email:
I am planning to use SNMP based monitoring, probably Observium, for all our data
centres, which means > 100 FreeBSD based hosts. The point of a monitoring/management
system is that anything flagged "red" is a real problem that needs attention and the default
state should be "everything super green". Things flagged "red" but "everybody knows
it can be ignored" bind a huge amount of brain capacity on behalf of the operators. Not good.


So what is going on here? What do these numbers actually mean? Where do they come
from? Are they artefacts of the SNMP implementation not taylored perfectly for FreeBSD
or are they some real metric that ends up interpreted wrong in the NMS (Observium)?

Thanks and kind regards,
Patrick
-- 
punkt.de GmbH
Patrick M. Hausen
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