I have a 25GB file that was incorrectly set as NTFS-compressed because the directory where it is had been marked as compressed when it was created. I am trying to decompress it. The file is currently in use by a Windows service process.

I tried using File Explorer at the directory level to clear the compression attribute; I clicked OK, but it came back in a few seconds. Although the directory was marked as not compressed, the file was still compressed and shows blue in the window.

I also tried using COMPACT /U – it also returns right away, and doesn't seem to decompress (although it appears to say that it did):

 E:\Services\MyService\Map>compact

 Listing E:\Services\MyService\Map\
 New files added to this directory will not be compressed.

27518828544 : 21974568960 = 1.3 to 1 C running.mmap
      235 :       235 = 1.0 to 1   test.txt

Of 2 files within 1 directories
1 are compressed and 1 are not compressed.
27,518,828,779 total bytes of data are stored in 21,974,569,195 bytes.
The compression ratio is 1.3 to 1.


E:\Services\MyService\Map>compact  /u *

 Uncompressing files in E:\Services\MyService\Map\

running.mmap [OK]

1 files within 1 directories were uncompressed.


E:\Services\MyService\Map>compact

 Listing E:\Services\MyService\Map\
 New files added to this directory will not be compressed.

27518828544 : 22014078976 = 1.3 to 1 C running.mmap
      235 :       235 = 1.0 to 1   test.txt

Of 2 files within 1 directories
1 are compressed and 1 are not compressed.
27,518,828,779 total bytes of data are stored in 22,014,079,211 bytes.
The compression ratio is 1.3 to 1.

Why is this happening? Is the system working in the background to decompress the file, or is it ignoring my request? This is Windows 2003 Server.