Calculating single-instance sharing ratio for a database LUN

This topic describes how to calculate the single-instance sharing ratio used to calculate the expected maximum size for an Exchange database LUN.

Single-instance sharing ratio for a new Exchange installation

For a new installation of Microsoft Exchange, use the value 1.5 for your single-instance sharing ratio.

Note
After you have a more mature installation, recalculate the ratio using the procedure below.

Use the following procedure to calculate the single-instance sharing ratio for your installation.

Use these guidelines when calculating the single instance ratio:

Track the ratio over time during peak production times; then choose the lowest ratio value recorded.
If you obtain different ratio values for different databases within a storage group, choose the lowest value for that storage group in your calculation.

To calculate the single-instance sharing ratio for your installation, complete the following steps.

Step	Action
1	Run the Windows Performance Monitor utility (also known as "Perfmon").
2	Right-click the graph and select Add Counters. Result The Add Counters dialog box is displayed.
3	In the Performance Object drop-down list, select the performance object MSExchangeIS Mailbox.
4	In the Select Counter From List option, select Single Instance Ratio.
5	Select all databases in the instances list for the storage group you are measuring.
6	Click Add.