Microsoft 1 manual Online Backups, Message Deletion and Online Defragmentation

Chapter 2: Capacity and Availability Management 27

scenario, the online maintenance occurs during the night (by default) when very few users are logged on, so the load on the Active Directory servers should be very low. The extra domain controller load created by online maintenance should not be a problem in this scenario.

If Exchange 2000 is installed in a global data center, serving customers from multiple time zones, the default online maintenance time could become an issue. The effect that online maintenance has on Active Directory is proportional to the number of users in each of the server’s databases. A check for a deleted mailbox is performed against each user in a database. Thus, if you have 10,000 users in a database, it will perform 10,000 LDAP searches against Active Directory at the beginning of that database’s online maintenance. If Active Directory servers are under moderate load at all times, it is necessary to stagger the online maintenance (set each database to start maintenance at a different time on the server-configuration object). This is especially critical if you have hundreds of thousands of users spread across dozens of servers and hundreds of databases.

Message Deletion and Online Defragmentation

These are very disk-intensive tasks and only affect the server on which the maintenance is being run. During this portion of online maintenance, the server might be perceived by users as sluggish if many databases are set to perform online maintenance at the same time. Again, in corporate scenarios this would occur at night where the server can easily handle the extra load. In a global data center, it might be a good idea to stagger the databases (in respect to each other on a single server) to spread the disk-intensive tasks over a greater amount of time.

Defragmenting the database consists of 18 separate tasks. After a task has started, it must complete fully before the process exits. Therefore, online maintenance can run over the time window. The next task will execute during the next online maintenance window. Depending upon the run window and the backup schedule, it might take a number of days before a full defragmentation completes.

Online Backups

Online backups complicate online maintenance even further. Backing up an Exchange 2000 database halts the maintenance of any database within that storage group, although it will restart if the backup is finished before the maintenance interval has been passed. If you have two databases in a single storage group and one is running online maintenance, the online defragmentation on the database that is running online maintenance will stop when a backup is started against either database.