When items are removed from the Exchange database, the space that is
freed up in the database is called white space. Exchange will use the available
white space in its database for new database content before having to grow the
size of the database.
With Exchange 2007 and older versions, one of the key elements that an
Exchange administrator needed to keep an eye on, and caused confusion for newcomers
to Exchange was the amount of white space in the database.
This is reported as free space in the event viewer via event ID 1221
during the night and is the result of content being removed from the database
by the online maintenance process.
With Exchange 2010, the behavior of the database has changed.
Instead of performing an online maintenance during a fixed time window,
it now does it constantly. This means that content that has passed the deleted
item retention period, is removed from the database shortly afterwards, rather
than waiting for the next online defrag window.
However because the process is running constantly, event ID 1221 isn’t
written to the event log. Therefore an administrator may not have a clue as to
how much of the database is white space, and how much is actual content.
This question can be easily answered, using EMS, as the amount of free
space in the database is available via get-mailboxdatabase -Status:
Get-MailboxDatabase -Status | Select Servername, Name,
AvailableNewMailboxSpace
This command will show you the name of the Server the database is
mounted on, the name of the database (which is unique across the Exchange org
with Exchange 2010) and the amount of space available in the database for new
content.
The result will be something along the lines of this:
ServerName Name
Available NewMailboxSpace
————– ——————– ————————
EXCH10 Mailbox
Database 27.75 MB (29,097,984
bytes)
The command used get-mailboxdatabase -status can provide quite a bit
of information about the databases in your Exchange org, use the |fl command to
see the full list.
Always remember that when you perform stress testing/sizing for your
Exchange 2010 environment, the IOPS created by this online maintenance should
be kept in mind. Jetstress is a tool to play with.
In Earlier versions of Exchange, admins used to run the switch eseutil /d for offline defragmentation on exchange databases.
To know this better, we need to discuss about event id: 1221 and its
relevance.
Event Type: Information
Event Source: MSExchangeIS
Mailbox Store
Event Category: General
Event ID: 1221
Date: 01/01/2005
Time: 00:04:16
User: N/A
Computer: SERVER
Description: The database
“First Storage Group\Mailbox Store (SERVER)” has 3.4 megabytes of free space
after online defragmentation has terminated.
Exchange has performed a routine maintenance and any old data that is
past the delete thresholds has been deleted from the database.
The space it has left behind has then been converted into “white
space”. No difference in the size of the database.
This “white space” will be used by Exchange, before expanding the
database any larger
Online defragmentation is an automated defragmentation process as a
part of its scheduled maintenance which we specify on a mailbox store level in
ESM where the actual database size remains the same wherein Offline
defragmentation is the process we use to shrink the database size removing
white spaces using the eseutil /d switch.
To determine the whitespace using eseutil command by using eseutil /ms
