The % Free Space performance counter displays the percentage of disk space that is available on a specific disk.

This alert indicates that the disk specified has less than 10 percent of free space available. Other symptoms you may experience when you reach this threshold are inability to move files to this disk, or inability to move mailboxes to this database, if this disk contains mailbox database files. If this is a Hub Transport or Edge Transport server, it may also experience back pressure.

To resolve this warning, do one or more of the following:

• Delete any unnecessary files from the disk.
  
  
• Move data that can be safely moved to another location.
  
  
• Add disk capacity to the server.
  
  
• If the disk that is specified contains mailbox or public folder database files, consider moving large mailboxes or public folders to a different database or a different server that has more disk space available, and then perform an offline defragmentation to compact the databases. For more information about how to do this task, see the following topics:
  
  
  • Create a Local Move Request
    
    
  • Move Public Folder Content from one Public Folder Database to Another Public Folder Database
    
    
  • Eseutil /D Defragmentation Mode.
    
    
• If the disk that is specified contains mailbox or public folder database log files, consider running backups more frequently. One of the functions performed at the end of a successful full or incremental backup is the truncation of transaction log files that are no longer needed for database recovery. For more information, see Understanding Backup, Restore and Disaster Recovery.
  
  
• If the disk that is specified contains Transport queue database or Transport database transaction logs, you may want to change the location of the queue database files if you are also experiencing queues backing up on this server. For more information, see Change the Location of the Queue Database.
  
  

If you are having difficulty resolving the issue, contact Microsoft Product Support. For information about contacting support, visit the Contact Us page of the Microsoft Support Web site.

If you are not already doing so, consider running the Exchange tools created to help you analyze and troubleshoot your Exchange environment. These tools can help make sure that your configuration aligns with Microsoft best practices. They can also help you identify and resolve performance issues, improve mail flow, and better manage disaster recovery scenarios. To run these tools, go to the Toolbox node of the Exchange Management Console. To learn more about these tools, see Managing Tools in the Toolbox.