Capacity Planning

This chapter shows you how to use VDM to do capacity planning.  Capacity planning is the process of projecting growth in resource usage to determine if new equipment has to be ordered.  To generate a capacity planning report, VDM needs four pieces of information:


. Current usage  VDM gets the current usage from its own data files.  You can select ACTUAL (allocated) usage, AVERAGE usage, MAXIMUM usage, or USED usage using the /USAGE qualifier. /USAGE=AVERAGE normally provides the best basis for projection and is the default.

. Period length  By default, the projection period length is 3 months.  Use the /PERIOD qualifier to specify a large or smaller number of months.

. Rate of increase  VDM uses as the projected rate of increase either:

A user-supplied percentage  You can specify a rate of increase using the /RATE=n qualifier where n is a per interval percentage increase.  It can be positive or negative and can include fractions (ie 2.4%)

The observed increase  If you don't specify a rate, VDM uses the percentage change between current usage and usage on some previous date to determine the rate of increase.  You specify the previous date using the /PREVIOUS qualifier.  Be sure to allow a reasonable length of time (a couple of months) between current and previous.  A difference of only a week will likely cause inaccurate projections.  VDM assumes that the observed rate of change applies to one projection interval, therefore you should specify a current and previous date which represents the number of months you have chosen for your projection interval.

4. The date used for the previous values If you don't specify a previous date VDM will determine the number of days in the period and check for data from that long ago. If a data file is not found for that date VDM will decrement the number of days by 1 and check again. It continues this way until it finds a data file. In this way VDM finds the oldest data file from the last period to use in its' calculations.

To present a concise, readable report, the rate of increase is truncated on the report to two decimal place (ie 23.423 becomes 23.42 and 56.878 becomes 56.87).  Internally, VDM carries the rate of increase to much more precision.  This means the projected increases may not appear to be consistent with hand calculations.

Projection calculation
VDM shows your current usage and project usage for five periods into the future.  It uses a simple (as opposed to compound) rate of growth when it is projecting growth.  Projections are truncated to the nearest block.

You can specify a sequence using the /SEQUENCE qualifier, summarize the data using the /SUMMARY qualifier and select disk drives using the /DISK qualifier.  Refer to the previous chapter "Generating Usage Reports" for more information on these qualifiers.


Examples

$ VDM  /REPORT=CAPACITY /PREVIOUS=01_NOV_96 /SEQUENCE=USERNAME -
    /SUMMARY
Produce a capacity planning report by username for all disk drives using the observed difference between current usage and November 1st, 1993 as the projected rate of increase.  Since type of usage is not specified, average usage is used.  The default interval of 3 months is used.


$ VDM /REPORT=CAPACITY /DISK=(DRA1:) /RATE=2 /SEQUENCE=UIC -
    /PERIOD=4
Produce a capacity planning report by UIC for DRA1: using a specified rate of increase of 2% per interval, using a 4 month interval.  Since type of usage is not specified, average usage is assumed.


$ VDM  /REPORT=CAPACITY /USAGE=ACTUAL /SEQUENCE=OWNER -
    /SUMMARY     /RATE=1.6
Produce a capacity planning report by owner for all disk drives at a rate of 1.6 percent.  Since /PREVIOUS was not specified VDM will find the oldest data file that is one period old or more recent.