vCenter Server and ESX/ESXi hosts use data counters to query for statistics. A data counter is a unit of information relevant to a given object.

For example, network metrics for a virtual machine include one counter that tracks the rate at which data is transmitted and another counter that tracks the rate at which data is received across a NIC instance.

To ensure performance is not impaired when collecting and writing the data to the database, cyclical queries are used to collect data counter statistics. The queries occur for a specified collection interval. At the end of each interval, the data calculation occurs.

Each data counter is comprised of several attributes that are used to determine the statistical value collected. Data Counter Attributes lists data counter attributes.

Data Counter Attributes

Attribute

Description

Unit of Measurement

Standard in which the statistic quantity is measured. One of:

KiloBytes (KB) – 1024 bytes

KiloBytes per second (KBps) – 1024 bytes per second

Kilobits (kb) – 1000 bits

Kilobits per second (kbps) – 1000 bits per second

Megabytes (MB)

megabytes per second (MBps)

megabits (Mb), megabits per second (Mbps)

megahertz (MHz)

microseconds (µs)

milliseconds (ms)

number (#)

percent (%)

seconds (s)

Description

Text description of the data counter.

Statistics Type

Measurement used during the statistics interval. The statistics type is related to the unit of measurement. One of:

Rate – Value over the current statistics interval

Delta – Change from previous statistics interval.

Absolute – Absolute value (independent of the statistics interval).

Rollup Type

Calculation method used during the statistics interval to roll up data. This determines the type of statistical values that are returned for the counter. One of:

Average – Data collected during the interval is aggregated and averaged.

Minimum – The minimum value is rolled up.

Maximum – The maximum value is rolled up.

The Minimum and Maximum values are collected and displayed only in collection level 4. Minimum and maximum rollup types are used to capture peaks in data during the interval. For real-time data, the value is the current minimum or current maximum. For historical data, the value is the average minimum or average maximum.

For example, the following information for the CPU usage chart shows that the average is collected at collection level 1 and the minimum and maximum values are collected at collection level 4.

Counter: usage

Unit: Percentage (%)

Rollup Type: Average (Minimum/Maximum)

Collection Level: 1 (4)

Summation – Data collected is summed. The measurement displayed in the chart represents the sum of data collected during the interval.

Latest – Data collected during the interval is a set value. The value displayed in the performance charts represents the current value.

Collection level

Number of data counters used to collect statistics. Collection levels range from 1 to 4, with 4 having the most counters.