How to remove Windows NTFS Compression from Oracle Database datafiles? We know Windows NTFS compression on Oracle Database datafiles is a bad idea. 

See here and here.

It prevents Asynchronous Random Disk I/O which can increase the risk of corruption and generally slow down the database.

However, we have some Oracle databases (11g &amp; 12c) on Windows Server 2012 R2 servers with Windows file compression on the datafiles. How do we safely deactivated this file compression? Are there any watch-outs?

Thanks.
As Paparazzi said for MSSQL, just shutdown the database and then decompress the files and startup again.  If your architecture allows, you could offline a tablespace at a time and then just decompress the datafiles for that tablespace.  Eventually though you will need do do the system tablespace and will need to shutdown the whole system.