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Q96386: Cannot Lower Estimated Compression Ratio with DoubleSpace

Article: Q96386
Product(s): Microsoft Disk Operating System
Version(s): MS-DOS:6.0,6.2,6.22
Operating System(s): 
Keyword(s): 
Last Modified: 26-NOV-1999

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft MS-DOS operating system versions 6.0, 6.2, 6.22 
-------------------------------------------------------------------------------

This information applies to both Microsoft DoubleSpace and Microsoft
DriveSpace. For MS-DOS 6.22, use DRVSPACE in place of DBLSPACE for commands
and filenames.

SYMPTOMS
========

DoubleSpace doesn't allow you to lower the estimated compression ratio (ECR).

CAUSE
=====

When you lower the ECR, you effectively reduce the size of the compressed drive.
Reducing the size of the compressed drive requires reducing the size of the file
allocation table (FAT). If there is an entry in use near the end of the FAT,
DoubleSpace cannot reduce the size (lower the ECR).

The following are examples of conditions that can prevent DoubleSpace from
lowering the ECR:

- Lost allocation units at the end of the compressed drive

- Heavily fragmented files on the compressed drive

- A file (with Hidden and/or System attributes set) stored at the end of the
  compressed drive

WORKAROUND
==========

To correct the lost allocation unit problem, run ScanDisk on the compressed
drive (if you are using MS-DOS 6.0, run CHKDSK /F).

To correct the fragmented drive problem, run DEFRAG /F /H on the compressed
drive.

To correct the hidden-system file problem:

1. Use the DIR command to search for system files on the compressed drive. For
  example, if your compressed drive is drive C, type "dir c /s /as /p" (without
  the quotation marks) at the MS-DOS command prompt and then press ENTER. Make
  note of the files that are listed.

  The following chart lists programs that are known to write system files at the
  end of a drive:

  Program name                  Program filename      System file created
  -----------------------------------------------------------------------

  Microsoft MS-DOS Mirror           MIRROR.COM              MIRORSAV.FIL
  Central Point Mirror              MIRROR.COM              MIRORSAV.FIL
  Symantec Norton Image             IMAGE.EXE               IMAGE.IDX
  Symantec Norton Format Recover    FR.EXE                  FRECOVER.IDX
  Microsoft MS-DOS 5.0 Undelete     MIRROR.COM              PCTRACKR.DEL
  Microsoft MS-DOS 6.0/6.2 Undelete
   - Delete Tracker                 UNDELETE.EXE            PCTRACKR.DEL
   - Delete Sentry                  UNDELETE.EXE            CONTROL.FIL
  Central Point Undelete
   - Delete Tracker                 UNDELETE.EXE            PCTRACKR.DEL
   - Delete Sentry                  UNDELETE.EXE            CONTROL.FIL

2. Use ATTRIB to remove the file attributes on the system files you found in
  step 1. For example, if you have a Mirror file on drive C, type the following
  at the MS-DOS command prompt and then press ENTER:

  " attrib -r -s -h c:\mirorsav.fil" (without the quotation marks)

  NOTE: If the system files you found are used by a delete-tracking program
  (refer to the table in step 1), you need to reboot your computer without
  loading the corresponding program file before you change the file attributes
  on the system file. To do so, reboot your computer and press F5 when the
  "Starting MS-DOS..." prompt is displayed.

3. Run Microsoft Defragmenter on the compressed drive. Change to the compressed
  drive and type "defrag /f /h" (without the quotation marks) at the MS-DOS
  command prompt.

You should now be able to lower the ECR on the DoubleSpace-compressed drive.

If you were able to successfully lower the ECR on the compressed drive, reset the
file attributes on the system file addressed in step 2. For example, type the
following at the MS-DOS command prompt and then press ENTER:

  " attrib +r +s +h c:\mirorsav.fil" (without the quotation marks)

NOTE: The DoubleSpace ECR is not based solely on the expected compressibility of
new data; it is also dependent on the size of the compressed volume file (CVF).
You may need to resize the compressed drive to change the ECR to the desired
value.



Additional query words: 6.00 6.20 double space drive

======================================================================
Keywords          :  
Technology        : kbMSDOSSearch kbMSDOS622 kbMSDOS620 kbMSDOS600
Version           : MS-DOS:6.0,6.2,6.22

=============================================================================

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