Explanation of the Enterprise Vault (EV) archiving strategy 'Based on age and quota'

Problem

How does the Enterprise Vault (EV) archiving strategy 'Based on age and quota' work?

Solution

This setting is configured on the Archiving Rules tab of the Mailbox policy. To find the setting do the following:

• Open the Enterprise Vault (EV) Vault Administration Console (VAC)
• Expand Site - Policies - Exchange - Mailbox
• Double click on the relevant policy
• Select the Archiving Rules tab and you will see the screen as below:

The Based on age and quota setting performs archiving both on the age of items and on keeping a percentage of each user's Exchange mailbox storage limit free. The archiving task performs age based archiving first and then quota if needed. If age based archiving does not make the required percentage of mailbox storage limit free, archiving continues until the required percentage is reached.

For example, if the strategy is set to archive Age based items older than 6 months and Quota based storage of 15% free then the following will occur:

1. The archiving task will archive all items older than 6 months first. Note:  The Override settings options will affect which items are archived. 

2. If the mailbox has less than 15% free space available after age based archiving is performed the archiving process will continue until there is at least 15% free in the mailbox. 

For the Age and Quota strategy to work EV estimates the space that will be saved when archiving the messages. EV takes into account the space that will be released by currently pending items. Counting the space saved by pending items allows quota archiving to perform multiple passes.

The shortcut size estimations dictate how accurately EV hits the quota target. If EV over estimates how much space it saves then enough will not be archived
If EV underestimates then too much will be archived. There are settings that can be altered to tune the shortcut estimations.

Shortcut Size Estimations

1. Where shortcuts are not being created and and the original items are being deleted there is a saving equal to the size of the item.

2. Where shortcuts replace items using custom settings the size is calculated as follows:

• Base item 3KB
• Plus 3KB for Banner
• Plus 1KB for Recipient Information
• Plus the number of characters to keep x 1 (adjustable via multiplier)

3. Where shortcuts replace items but the original body is kept:

• Base item 3KB
• Plus 5KB for the average body
• Plus 1KB for the recipient information

4. For calendar items where stripping attachments:

• Base item 3KB
• Plus 5KB for the average body
• Plus 1KB for the recipient information

In all cases where the shortcut estimate is larger than the original item, we set the estimate to be equal the size of the item.

The following registry keys can be used to tweak the shortcut size estimations:

On a 32-bit installation of Windows:

HKEY_LOCAL_MACHINE\SOFTWARE\KVS\Enterprise Vault\Agents

On a 64-bit installation of Windows:

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\KVS\Enterprise Vault\Agents

ShortcutCalcBaseItemSize (Bytes)
ShortcutCalcBannerSize (Bytes)
ShortcutCalcBodySizeMultiplier (int)
ShortcutCalcAverageBodySize (Bytes)
ShortcutCalcRecipientSize (Bytes)
 

An archiving report can be run from the Mailbox Archiving task to determine how much free space is in the mailbox.  The % of Quota free column will show the number for quota based archiving. The report output will be written to the <install_path>\Enterprise Vault\Reports\Exchange Mailbox Archiving.