Designing Mailbox Sizing & Database Configuration – Exchange 2010

To design mailbox size, you must first understand the business needs that drive mailbox size. The business needs for mailbox storage vary depending on the type of users

Questions to ask:

To select an appropriate mailbox size, you should consider:

  • What types of messages do users need to keep for an extended period of time?
  • How long do messages need to be kept?
  • How does the volume of messages stored vary by job role?
  • What is the cost of increasing storage size versus the cost of not having content easily available?

Cached Exchange Mode

When you deploy Office Outlook 2003 or later, you can use Cached Exchange Mode. Cached Exchange Mode places a copy of the mailbox on the client computer, and synchronizes the changes with the Exchange Server. After the mailbox is synchronized on the client computer, all requests to view or modify a message or calendar item are performed on the locally cached copy of the mailbox.

In previous versions of Exchange Server, using Exchange Cached Mode increases the Mailbox server performance, because a lesser number of requests are submitted to the Mailbox server. In Exchange Server 2010, using Exchange Cached Mode does not increase Mailbox server performance, because of the changes in storage architecture.

Users with a slow connection to the Exchange server will typically experience a performance improvement when using Cached Exchange Mode. However, as the size of the cached mailbox increases, performance decreases. Increased random access memory (RAM) and faster disks in client computers can increase the performance of locally cached mailboxes.

Personal Archives

Personal Archives are a new feature in Exchange Server 2010. Personal Archives are designed to address the problems encountered when you archive data to PST files. PST files are problematic, because they are difficult to manage and may be stored in a location that is not backed up. This increases the risk that messages will be lost.

The intent of Personal Archives is to replace PST files. Messages are archived to the archive mailbox rather than a PST file. The Personal Archive is located in the same mailbox database as the associated mailbox. Therefore, a Personal Archive decreases the size of a user mailbox, but not the size of a mailbox database. In fact, if PST files are imported, overall mailbox database size may increase.

When you use Cached Exchange Mode and Personal Archives at the same time, you reduce the amount of data cached on the client. Only the content in the user mailbox is cached locally on the client, and the content in the archive mailbox is not cached. This can increase overall client performance, while still providing access to archived data when required.

Some additional considerations:

Do not assume that the mailbox quota size is the amount of disk space that is used for each mailbox. Many mailboxes might not be filled to capacity. Find out what the actual usage is for mailboxes, and then be prepared for the possibility that mailboxes will grow to the maximum size of the quota.

Databases never shrink automatically. If you have a large mailbox database that you remove users from, the mailbox database does not shrink automatically. Instead, empty white space remains inside the database file. To physically shrink the database on disk, you must perform an offline defragmentation.

Deleted item retention has an affect on mailbox database size. If you increase the deleted item retention limit from the default value of 14 days, then the size of the mailbox database increases. These items are not included when you view mailbox size.

Deleted mailbox retention has an effect on mailbox database size. If you increase the deleted mailbox retention limit from the default of 30 days, then the size of the mailbox database increases.

Post Office Protocol (POP3) clients may remove messages immediately. Unlike Messaging Application Programming Interface (MAPI) and Outlook Web App clients, POP3 clients are sometimes configured to delete messages from the mailbox after they are downloaded to the client. If you configure the POP3 clients in this way, mailboxes will be much smaller than those used by the MAPI and Outlook Web App clients.

Mailbox Server Database Configuration

In previous versions of Exchange Server, it is recommended that you keep the log files and database on separate disks. In case of disk failure where the database is lost, you still have the log files available after a restore, and can replay them to recover messages received since the last backup. In Exchange Server 2010, the same recommendation still applies for small environments that do not use DAGs. However, if a database is replicated, you do not need to keep the transaction logs and database separate, because a different replica is used instead of recovering from a backup.

Disk Space Considerations

When you calculate the disk space requirements for a database on a Mailbox server, you need to consider more than just the mailbox databases. In most cases, you may want to enable indexing on databases to speed up searches. Each index uses approximately 5 percent of the mailbox database disk space. This index is placed in the same location as the database.

You can use a recovery database in a variety of recovery scenarios to extract mailbox data. To use a recovery database, you must have sufficient disk space available to restore the database and transaction logs.

Exchange Server Editions

Exchange Server 2010 does not limit the size of databases based on the edition of Exchange Server 2010 that you have selected. The only database limitation based on the edition of Exchange Server 2010 is the number of databases that are supported on each server. Exchange Server 2010 Standard edition supports up to five databases on each server, while Exchange Server 2010 Enterprise edition supports up to 100 databases on each server.

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