Windows NT NTFS Directory Compression

Compression utilities were once big sellers to PC users. At that time, the
utility would compress at a partition level. The BIG downside was that a minor
corruption could result in the loss of all data on the partition. You don’t see
these add-ons much anymore. Partly because large hard drives are cheap and
partly because of too many failures.

Microsoft shipped NT4 with directory level compression for partitions
formatted with the NTFS. If you need to free up space, I have seen very few
problems. Its a good solution. It can actually speedup access of data files. If
you are interested in trying this, I recommend compressing data directories and
not compressing directories containing many executables.

To compess a directory (or partition):

  • Start Explorer
  • Right-click the directory
  • Select Properties
  • Check the Compress option
  • Click Apply and Explorer gives you the option to apply the compression
    subdirectories by checking the Also compress
You can undo the compress up unchecking the Compress option.

If you have the Windows NT Resource Kit, it includes compact.exe which you can use from the commandline to view or
change the compression of individual files and/or directories.

compact /? gives the following help listing:

Displays or alters the compression of files on NTFS partitions.

COMPACT [/C | /U] [/S[:dir]] [/A] [/I] [/F] [/Q] [filename […]]

/C Compresses the specified files. Directories will be marked
so that files added afterward will be compressed.
/U Uncompresses the specified files. Directories will be marked
so that files added afterward will not be compressed.
/S Performs the specified operation on files in the given
directory and all subdirectories. Default “dir” is the
current directory.
/A Displays files with the hidden or system attributes. These
files are omitted by default.
/I Continues performing the specified operation even after errors
have occurred. By default, COMPACT stops when an error is
/F Forces the compress operation on all specified files, even
those which are already compressed. Already-compressed files
are skipped by default.
/Q Reports only the most essential information.
filename Specifies a pattern, file, or directory.

Used without parameters, COMPACT displays the compression state of
the current directory and any files it contains. You may use multiple
filenames and wildcards. You must put spaces between multiple

If I want to compress a large data file, bigfile.txt, the command would be:

compact /c bigfile.txt

If you try compression on an NTFS partition and get the error message:

The file system does not support compression.

You will get this error if NTFS partition has very large cluster sizes, that
is, greater than 4096. Chkdsk will give you the cluster size (it calls it
allocation unit) at the end of its listing. There is no dynamic, inplace
solution. Backup. Format the partition using the /a:4096
. This issue is discussed in q171892 .

NTFS Tips:

Managing Shared Resources and Resource Security
Between FAT and NTFS

versus NTFS Permissions

Getting the Most from IIS Security
Security, Part 2: Implementing NTFS Special Permissions on Your Web Site

Getting the Most from IIS Security
NTFS Permissions
Cancel an NTFS conversion

NT equivalents of
NetWare Rights

NTFS from DOS, Win95 or Win98 using NTFSDOS driver

NTFS Last Access TimeStamp

xcopy – keep attributes

How To Remove Files
with Reserved Names such as LPT1 or PRN

NTFS Metadata files
Disable NTs 8.3 aliases for
LFNs under NTFS

displays which NTFS files have alternate streams content

VolumeID changes NT and FAT volume

Create a NTFS
partition over 4GB during installation

Windows NT NTFS Directory

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