Cannot Lower Estimated Compression Ratio with DoubleSpace (96386)


The information in this article applies to:

  • Microsoft MS-DOS operating system 6.0
  • Microsoft MS-DOS operating system 6.2
  • Microsoft MS-DOS operating system 6.22
This article was previously published under Q96386
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 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

    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

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.
Modification Type:MajorLast Reviewed:11/26/1999
Keywords:KB96386
©2002 Microsoft Corporation. All rights reserved.