Assume that you use Microsoft SQL Server 2014. When you use full-text index, you may notice that the index works well, but the files created by full-text search (FTS) in subfolder \FTDATA\FILTERDATA are not automatically removed as they should.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
This issue is fixed in the following cumulative update for SQL Server:
About cumulative updates for SQL Server:
Each new cumulative update for SQL Server contains all the hotfixes and all the security fixes that were included with the previous cumulative update. Check out the latest cumulative updates for SQL Server: