Collection Intervals

Collection intervals determine the time period during which statistics are aggregated and rolled up, and the length of time the statistics are archived in the vCenter database.

By default, vCenter Server has four collection intervals: Day, Week, Month, and Year. Each interval specifies a length of a time statistics are archived in the vCenter database. You can configure which intervals are enabled and for what period of time. You can also configure the number of data counters used during a collection interval by setting the collection level. Together, the collection interval and collection level determine how much statistical data is collected and stored in your vCenter Server database.

Real-time statistics are not stored in the database. They are stored in a flat file on hosts and in memory on the vCenter Server systems. Hosts collect real-time statistics only for the host or the virtual machines available on the host. Real-time statistics are collected directly on a host every 20 seconds (60 seconds for ESX Server 2.x hosts). If you query for real-time statistics in the vSphere Client for performance charts, vCenter Server queries each host directly for the data. It does not process the data at this point. It only passes the data to the vSphere Client. The processing occurs in a separate operation. On hosts, the statistics are kept for one hour, after which 180 data points (15 -20 second samples) will have been collected. The data points are aggregated, processed, and returned to vCenter Server. At this point, vCenter Server archives the data in the database as a data point for the Day collection interval.

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.

Table 4 lists the default collection intervals available for the vCenter Server.

Table 4. Collection Intervals

Collection Interval/Archive Length	Collection Frequency	Default Behavior
1 Day	5 Minutes	Real-time statistics are rolled up to create one data point every 5 minutes. The result is 12 data points every hour and 288 data points every day. After 30 minutes, the six data points collected are aggregated and rolled up as a data point for the 1 Week time range. You can change the interval duration and archive length of the 1 Day collection interval by configuring the statistics settings.
1 Week	30 Minutes	1 Day statistics are rolled up to create one data point every 30 minutes. The result is 48 data points every day and 336 data points every week. Every 2 hours, the 12 data points collected are aggregated and rolled up as a data point for the 1 Month time range. You cannot change the default settings of the 1 Week collection interval.
1 Month	2 Hours	1 Week statistics are rolled up to create one data point every 2 hours. The result is 12 data points every day and 360 data points every month (assuming a 30-day month). After 24 hours, the 12 data points collected are aggregated and rolled up as a data point for the 1 Year time range. You cannot change the default settings of the 1 Month collection interval.
1 Year	1 Day	1 Month statistics are rolled up to create one data point every day. The result is 365 data points each year. You can change the interval duration and archive length of the 1 Year collection interval by configuring the statistics settings.