Topic Last Modified: 2005-11-18

The Microsoft® Exchange Server Analyzer Tool queries the Win32_Volume Microsoft Windows® Management Instrumentation (WMI) class to determine the value of the FreeSpace key for volume mount points used by the Exchange Server computer. If the value for FreeSpace, when divided by 1,000,000,000 and rounded up to the nearest whole number, is less than 4, a warning is displayed.

This warning indicates that less than 3 gigabytes (GB) of storage space is available for a volume mount point. In Exchange Server 2003, volume mount points (also known as NTFS file system junction points) are supported as a location for data storage in a clustered configuration when Exchange Server 2003 is installed on a computer running Microsoft Windows Server™ 2003, Enterprise Edition or Windows Server 2003, Datacenter Edition. With the NTFS Volume Mount Points feature, you can surpass the 26-drive-letter limitation. By using volume mount points, you can graft, or mount a target partition into a folder on another physical disk. Volume mount points are transparent to programs such as Exchange Server 2003.

Mount points are not supported in the following scenarios:

Regardless of whether a volume used by Exchange Server is a local physical disk, a logical volume, or a volume mount point, best practices for Exchange Server implementations are to have at least 50 percent free disk space available on all drives. As a general rule of thumb, Microsoft recommends a minimum of 25 to 30 percent of free disk space for Exchange maintenance such as tasks performed using database utilities such as Eseutil and Isinteg. In addition, for some maintenance operations, such as offline defragmentation, Microsoft recommends that you have 100 percent more free space than the amount you are defragmenting. For example, if you are defragmenting a 1 GB database, you should have at least 1 GB of free disk space available.

Having plenty of free disk space is also beneficial from a both a security and an availability perspective. A denial of service attack, a message loop, or a virus outbreak that is widespread can cause excessive consumption of disk space due to increased message traffic, transaction log activity, and so forth.

To correct this warning

  1. Investigate areas to reclaim disk space and increase available space.

  2. If disk space is extremely low, you should consider moving data to another Exchange Server computer or Exchange Virtual Server that is not space constrained. If not already done, setting mailbox limits can also be useful in managing disk utilization.

For more information about using volume mount points in an Exchange Server 2003 cluster, see the Microsoft Knowledge Base article 318458, "Volume Mount Point Support for an Exchange Server 2003 Cluster on a Windows Server 2003-based System" (

For more information about using volume mount points in a Windows Server 2003 cluster, see the Knowledge Base article 280297, "How to configure Volume Mount Points on a clustered server" (