Exchange databases run a defragmentation process once a day by default. This process rearranges mailbox store and public folder store data more efficiently, eliminating unused storage space. Exchange database online defragmentation occurs automatically as part of the database maintenance process. Online defragmenting is performed automatically at 2:00 AM every day by default. Online defragmentation makes additional database space available by detecting and removing database objects that are no longer being used. The defragmentation process provides more database space without actually changing the file size of the database.