This is the amount of free disk space remaining on the volume hosting the SmartEvent database, independent of the configured logical database capacity tracked elsewhere in this MIB. This catches the case where the SmartEvent database's logical capacity hasn't been reached but the underlying disk is nonetheless running out of physical space, for example because it's shared with other applications' logs, which the capacity and size fields alone wouldn't reveal. For example, disk space dropping to a few hundred megabytes free even while the SmartEvent database itself is well under its configured capacity would point to a different process on the same volume consuming space.