Understanding White Space in Exchange Mailbox DatabaseMustBeGeek

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Exchange Information Store does a very good job of managing mailbox database and white space in any given mailbox database. The size of mailbox database grows automatically but it won’t decrease automatically when you delete mailbox or it’s contents. However, you can manually reclaim the white space in Exchange Mailbox Database. In this article we will focus on understanding white space in Exchange Mailbox Database.

Understanding White Space in Exchange Mailbox Database

White space is like a buffer and is created when you create a mailbox database itself and may increase or decrease when you delete, migrate, or purge any mailbox or archives from mailbox database in Exchange Server. The mailbox database will reuse this white space for any new mailbox items or objects and when the white space is used it will also take up more disk space and allocate more space for white space within the mailbox database ultimately increasing the database size. The size of mailbox database grows automatically but it doesn’t decrease automatically when you delete mailboxes of a particular database. To better understand white space, let us assume that we have created a mailbox database DB01 on.D: drive which have total disk capacity of 100 GB. Let’s say the mailbox database contains many mailboxes and the size of mailbox database is now 90 GB.

Now, If we delete or migrate 10 GB worth of mailbox, the mailbox database size remains same at 90 GB but there will be a 10 GB of white space still being used by the database.

To check the amount of white space, you can type the following command in the Exchange management shell.

Get-MailboxDatabase -Status | Select Name, DatabaseSize, AvailableNewMailboxSpace

The above command only accounts the amount of free space available for new mailbox in the root tree of a mailbox database. It will not include any deleted or purged individual items, objects, indexes and tables under each mailbox. You can use the following command to get more accurate size of white space in a mailbox database.

ESEUTIL /MS D:\Path_to_DB\DB.edb

However, if you add new mailboxes or migrate existing mailbox having 5 GB of data then Exchange Information Store will reuse the white space. Now the white space is decreased to 5GB.

Once the white space is utilized almost completely by the mailbox database, then the Information Store will allocate more white space to the mailbox database increasing the overall total size of the mailbox database.