Installation guide

Using Collection Levels Effectively
Using collection level 1 is generally adequate for monitoring performance. There are some instances in which
you might need to collect more performance statistics, for example, to troubleshoot performance problems.
Before you increase the collection level for an interval, view charts in real-time. Viewing real-time data has less
impact on performance because metrics are retrieved directly from the source without being written to the
vCenter Server database.
If you change to collection level 3 or 4 to diagnose problems, reset the collection level to its previous state as
soon as possible. At collection level 4, try to limit the collection period to the Day interval to not have an impact
on the database. If you need to save the data for longer than one day, increase interval to two or three days
rather than using the Week interval. For example, if you need to record data over the weekend, set the interval
to three days. Use a week interval only when you need the duration to be more than three days.
Table 22-5 lists the circumstances in which you might want to increase the collection level for your vCenter
Server.
Table 22-5. Collection Level Scenarios
Use Collection
Level To do this
2
n
Identify virtual machines that can be co-located because of complimentary memory sharing.
n
Detect the amount of active memory on a host to determine whether it can handle additional virtual
machines.
3
n
Compare ready and wait times of virtual CPUs to determine the effectiveness of VSMP.
n
Diagnose problems with devices, or compare performance among multiple devices.
4
n
Determine whether a device is being saturated.
n
Troubleshoot errors.
How Metrics Are Stored in the vCenter Server Database
The metrics gathered for each collection interval are stored in their own database tables.
At the end of an interval, one of two things can occur.
n
If the next interval is disabled, the data in the table that is older than the interval duration is purged.
n
If the next interval is enabled, the data is aggregated into groups and is rolled up to the database table of
the subsequent collection interval. For example, the day interval has a 5 minute collection frequency, and
the week interval has a 30 minute collection frequency. When the day interval completes, it aggregates
the 5 minute queries into groups of six (equaling 30 minutes) and rolls the 30-minute data block to the
week interval database table. The day-old data is then purged from the database to make room for new
queries.
You control how long statistical data is stored in the vCenter Server database by enabling or disabling a
collection interval. When you disable a collection interval, all subsequent intervals are automatically disabled.
For example, when you disable the week interval, the month and year intervals are also disabled. Data is purged
at the end of the day interval cycle because no rollups can occur. The oldest data is purged first.
NOTE You must manually enable each collection interval to use it again. Also, you can only enable a collection
interval if all previous collection intervals are enabled. For example, to enable the month interval, the day and
week intervals must be enabled.
By default, statistics are stored in the vCenter Server database for one year. You can increase this to five years.
To save statistical data for longer than five years, archive it outside of the vCenter Server database.
Chapter 22 Working with Performance Statistics
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