Disk Space Needed to Save UNFORMAT Information (71585)

This article was previously published under Q71585


The following error message is displayed when the FORMAT command cannot find enough free space on the disk to save the UNFORMAT information:

Drive <x> error. Insufficient space for the MIRROR image file.
There was an error creating the format recovery file.
This disk cannot be unformatted.
Proceed (y/n)
Note: <x> refers to either drive A or B or any other external drive.

When the FORMAT command is used without the "/U" option, it tries to save the UNFORMAT information when reformatting a disk to the same density. The following is the minimum space required in the last 25 percent of the disk space for the FORMAT command to create a MIRROR image file:
   Disk Size       Capacity      Free Space Needed
   ---------       --------      -----------------

   5.25 inches     360K           7,168 bytes
   5.25 inches     1.2 MB        12,800 bytes
   3.5 inches      720K           8,192 bytes
   3.5 inches      1.44 MB       13,824 bytes


The FORMAT command in MS-DOS version 5.0 examines the disk to determine if it has already been formatted. If the disk has been formatted, the FORMAT command attempts to create a MIRROR image file before reformatting the disk. When FORMAT finds that there is not enough room on the disk to create a MIRROR image file, it displays the error message and gives you an option to continue with FORMAT. If you choose to continue, the MIRROR image file is not created, and the UNFORMAT command will not be able to recover the old information from the newly formatted disk.

A MIRROR image file contains the information that the UNFORMAT command needs to unformat the disk. MIRROR image files can also be created with the MIRROR command. For more information on MIRROR, FORMAT, and UNFORMAT, query on the following words:

mirror and unformat

The UNFORMAT information consists of Boot Sector, File Allocation Table, and Root Directory, which is stored in the MIRROR image file.

The requirement of free space in the last 25 percent of the disk space is imposed to prevent UNFORMAT from taking an extensive amount of time when trying to find the control file anywhere on the disk.

Modification Type: Major Last Reviewed: 7/30/2001
Keywords: KB71585