Smarts PM Calculates very High Utilization Values with HighUtilization Event

Products

• VMware

Issue/Introduction

Symptoms:
Smarts PM Calculates very High Utilization Values with HighUtilization Event

Environment

VMware Smart Assurance - SMARTS

Cause

There are several known defects in the SNMP Agents of various vendors where the high capacity (HC) 64-bit counters wrap to zero at the 32 bit mark. This is an incorrect behavior of the SNMP Agent devices.

Background
High Utilization calculations can use one of two sets of variables.  IfInOctets (OID: 1.3.6.1.2.1.2.2.1.10) and IfOutOctets  (OID: .1.3.6.1.2.2.1.16) were defined as 32-bit counters in the original MIB specifications from the IETF.  Because these counters were 32-bit, the maximum value they could hold was 2^32. As interfaces became faster, 2^32 was insufficient and network managers saw the values wrapping between polling cycles. Sometimes, the values could wrap several times between polls making these values unreliable at higher interface speeds. An extended Interface MIB was defined  to overcome the wrapping problem which included ifHCInOctets (OID .1.3.6.1.2.1.31.1.1.1.6) and ifHCOutOctets (OID: .1.3.6.1.2.1.31.1.1.1.10) as 64 bit counters.

When HC counters exist, Smarts uses them to calculate Utilization. Smarts has forumulas that handle a wrap of the counter gracefully. When any of the counter values decreases (and systemUpTime does not) Smarts regards this as a wrap and takes the difference between the max counter value and the last reading then adds the current reading and divides by the polling rate. For example, the ifInOctets formula for the wrapping of 32-bit counters is as follows:

((2^32 - LastValue) + CurrentValue)/PollTime

When HC counters exist, the ifHCInOctets formula for the wrapping of 64-bit counters is as follows:

((2^64 - Last Value) + CurrentValue)/PollTime

The problem described in this solution occurs because the 64-bit HC counters are wrapping at 32-bits.

Note: The default PollTime for Utilization variables is 240 seconds.

Resolution

As a defect in the SNMP Agent of the device, this issue cannot be resolved by EMC. Contact the device vendor for an update to the SNMP Agent. EMC Support does have a script available to assist with collection of data to confirm that the HC counters wrap at 32 bits instead of 64 bits. Contact EMC Support for more information on this script, and quote this solution ID.