A folder marked for NTFS compression does not prove that every file already inside it has the same compression state. This matters when you are checking a previous storage-saving change and its result seems inconsistent.

Work with a known data folder on an NTFS volume. Preserve an independent copy of important files before considering any changes. Avoid starting with Windows system folders, application databases or a drive whose reliability is already in doubt.

Separate the directory setting from its contents

Microsoft explains that a directory’s compression state controls whether files added to it are compressed automatically. Changing that state does not necessarily change the files that were already there. Inspect the existing files rather than relying on the parent folder alone.

In Command Prompt, move to the intended folder. This example uses a disposable test location that you have created:

cd /d "C:\CompressionTest"
compact

With no parameters, compact displays the current directory and its contained files’ compression states. The first line changes the working location; it does not create the folder. If that step fails, stop instead of inspecting an unintended directory.

Read the displayed path before interpreting the results. Pick a few known older files and compare them with files deliberately added after the folder setting was established. Record what is actually reported.

Account for the inspection’s limits

An ordinary listing is not a recursive inventory of every nested folder. The documented /s option extends the chosen operation through subdirectories, while /a includes hidden and system files omitted by default. Understand the command’s switches before broadening its scope.

The /c and /u switches change compression. Keep them out of an information-gathering command, and do not copy a whole-volume example when the question concerns one project folder.

If existing files need a deliberate change, define that set and test copies through their normal applications before a larger operation. Recheck both the directory and individual file states afterwards. Compression settings are storage properties; they do not replace a backup or establish that the documents are readable.

Sources: Microsoft compact command.