The
Exchange Server storage system is a database and requires routine
maintenance to perform efficiently and prevent failures. In the old
days, this required routine maintenance and planned downtime. Exchange
Server 2010 does away with all that by fully automating the routine
maintenance tasks of defragmentation and compaction. Exchange Server
2010 has advanced the health of the messaging system through the
introduction of the following:
Continuous online database defragmentation
Continuous online database compaction
Continuous online database contiguity maintenance
This has eliminated the need for routine offline database maintenance, which dramatically reduces the need for planned downtime.
As messaging
environments have evolved from “nice to have” to “business critical,”
database maintenance has evolved from “should be done” to “must be
done.” Any database that is not regularly maintained will suffer from
some level of corruption and, if left unchecked, might fail. Hence, the
automatic daily maintenance that Exchange Server 2010 performs is
invaluable to maintaining a healthy messaging environment.
However, there are other potential causes of database corruption. These include the following:
Improper shutting down of the system, including unexpected power outages
A poorly maintained disk subsystem
Hardware failures
Failure to use or review systems or operational management tools
Manual modification of Exchange Server databases
Deletion of Exchange Server transaction logs
Sometime, administrators still need to perform manual maintenance using the isinteg and eseutil tools.
Automatic Database Maintenance
Exchange Server
2010 automatically performs database maintenance procedures on a nightly
basis during the scheduled maintenance window. Exchange Server 2010
performs two distinct activities: Online Maintenance (OLM) and Online
Defragmentation (OLD). OLM starts by default at 1:00 a.m. every day,
whereas OLD is continuous.
Note
This
is different than in Exchange Server 2007, in which OLD ran during the
OLM process. This led to a fragmented database during operations with
the attendant drop in performance.
The following tasks are automatically performed by these processes (OLM and OLD):
Cleanup (deleted items/mailboxes)— Cleanup also happens during OLM. Cleanup is performed at run time when hard deletes occur.
Space Compaction— Database is compacted and space reclaimed at run time. Auto-throttled to avoid performance impact on end users.
Maintain Contiguity—
Database is analyzed for contiguity and space at run time and is
defragmented in the background. Auto-throttled to avoid performance
impact on end users. The contiguity maintenance is new to Exchange
Server 2010 and improves performance significantly.
Database Checksum—
There are two options for the database checksum tasks: either run the
background 24x7 (the default) or run during the OLM window. In both
cases, the task runs against both Active and Passive copies of the
database.
By default, the OLM
maintenance schedule is set to run daily from 1:00 a.m. to 5:00 a.m.
Because the maintenance cycle can be extremely resource intensive, this
default schedule is intended to perform the maintenance during periods
when most of an organization’s mail users are not connected. However,
organizations should also take their Exchange Server backup schedules
into consideration.
The OLD task runs continuously but is auto-throttled to prevent impact to the end user.
Taken
together, the new automatic maintenance regime is much more effective at
keeping the database healthy and performing. In particular, the
contiguity maintenance of Exchange Server 2010 reduces the I/O of the
database immensely.
Configuring Database Maintenance Schedules
Administrators
can stagger the maintenance schedules for different databases. For
example, database 1 might have the maintenance cycle performed from 1:00
a.m. to 2:00 a.m., and the next store from 2:00 a.m. to 3:00 a.m., and
so on. To view or change the default maintenance schedule on a database,
perform the following steps:
1. | Open the Exchange Management Console.
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2. | In the console tree, expand Organization Configuration and select Mailbox.
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3. | Select the Database Management tab and then select the appropriate database.
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4. | In the action pane, click Properties.
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5. | On the Maintenance tab, locate the Maintenance Schedule.
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6. | To
change the default schedule, select one of the options from the
drop-down box, or click Customize to create your own schedule.
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