I'm currently monitoring 150 network devices (Brocade switches/routers) with only some key information (uplinks, cpu, temperature) Overall I have ~3500 SNMP items and new values per second is around 35. So everything seem to be ok.

Using SNMPv3 on all checks results in a lot of network errors in the server log. Ruffly I have every second a entry like that:

31229:20120521:104212.070 SNMP item [.1.3.6.1.2.1.2.2.1.16.65] on host [SDEGFE17] failed: first network error, wait for 15 seconds
31250:20120521:104212.270 resuming SNMP checks on host [PTEGFE08]: connection restored
31231:20120521:104213.114 SNMP item [.1.3.6.1.2.1.2.2.1.16.66] on host [SDEGFE17] failed: another network error, wait for 15 seconds
31249:20120521:104218.291 resuming SNMP checks on host [FAEGFE06]: connection restored
31230:20120521:104220.432 SNMP item [.1.3.6.1.2.1.2.2.1.16.65] on host [PTEGFE09] failed: first network error, wait for 15 seconds
31232:20120521:104222.501 SNMP item [.1.3.6.1.2.1.2.2.1.20.65] on host [PTEGFE09] failed: another network error, wait for 15 seconds
31248:20120521:104222.516 SNMP item [.1.3.6.1.2.1.2.2.1.10.3] on host [TEEGFE02] failed: first network error, wait for 15 seconds
31238:20120521:104223.569 SNMP item [cpuUtil1Min] on host [STGEGFE01] failed: first network error, wait for 15 seconds
31249:20120521:104228.342 resuming SNMP checks on host [SDEGFE17]: connection restored

The update queue has also a lot of entries up to 5min waits.

Then I changed all my SNMP items to SNMPv2 and the errors are gone, not a single network error anymore! Update queue is also empty!

I did a quick test to be sure that the network device is not charged to much with those SNMPv3 settings but I could easely retrieve 100 values within seconds without a single error.

The zabbix server itself is also under no load at all