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Q171892: Err Msg: The File System Does Not Support Compression

Article: Q171892
Product(s): Microsoft Windows NT
Version(s): WinNT:3.51,4.0
Operating System(s): 
Keyword(s): kbsetup
Last Modified: 10-AUG-2001

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The information in this article applies to:

- Microsoft Windows NT Workstation versions 3.51, 4.0 
- Microsoft Windows NT Server versions 3.51, 4.0 
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SYMPTOMS
========

When you try to compress an NTFS partition using Windows NT Explorer, the option
is unavailable while looking at properties or, while using the Command Line
utility Compact.exe, you receive the error message:

  The file system does not support compression

For example:

  H:\compact /c *.* /s

  Compressing files in H:\

  Apps [ERR]
  Apps: The file system does not support compression.

  0 files within 1 directories were compressed.
  0 total bytes of data are stored in 0 bytes.
  The compression ratio is 1.0 to 1.

CAUSE
=====

The partition is a very large partition, and when the partition was formatted,
it was formatted with a cluster size greater than the default size of 4,096
bytes. NTFS compression is not supported for allocation unit sizes above 4k
bytes

You can verify what the allocation unit size is by doing a CHKDSK at the command
prompt and look at the bytes in each allocation unit.

RESOLUTION
==========

To resolve this problem, you must backup your data, then reformat the NTFS
partition using a cluster size of 4,096 bytes or less.

You can use one of three methods to reformat:

- Start Windows NT Explorer, right-click on the drive icon, select format, and
  then set the allocation unit size to 4,096 or less.

- Start Disk Administrator, right-click on the partition, select format, and
  then set the allocation unit size to 4,096 or less.

- Use the FORMAT command with the /A:size option and format it for an
  allocation unit size 4,096.

  For example,

  format c: /A:4096

MORE INFORMATION
================

NTFS needs to process an entire compression unit at a time when writing
compressed files, where a compression unit consists of 16 clusters.

Windows NT memory management's largest paging write size is 64 KB and Windows NT
limits operations to the maximum memory management transfer size.

This results in a maximum cluster size that can be manipulated within the
compression code to 4 KB. [64 KB/16 clusters = 4 KB per cluster]

Some defrag software also uses the same compression code and may have the same
limitation of 4 KB clusters.

Additional query words: compress ntfs

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Keywords          : kbsetup 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT351search kbWinNT400search kbWinNTW351search kbWinNTW351 kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS351 kbWinNTS351search
Version           : WinNT:3.51,4.0
Issue type        : kbprb

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