Backup Failure Because of 4 GB File Size Limitation

I started a backup of the Microsoft Exchange Information Store using the Windows Backup Utility last night. But, when I checked the status of the backup this morning, I found it had failed due to the size of the backup file reaching 4 GB in size. I saw the message "You have either run out of space, or the backup file (.bkf) is too large for this disk. Note: If this disk is formatted with FAT32, the maximum possible size for the backup file is limited to 4 GB."

Backup Utility 4GB error

Clicking on OK shows that the backup failed after backing up 4,295,194,412 bytes of data, which is 4 GB of data (4,295,194,412 bytes / 1,024 bytes/kilobyte / 1,024 kilobytes/megabyte / 1,024 megabytes/gigabyte).

Backup Progress failure status

The log file showed "End of Media encountered while backing up to non-removable media" and "The operation did not successfully complete."

I had been backing up the Exchange Information Store, which holds all users' email on the Exchange server, to an NTFS-formatted external USB drive, but recently swapped that drive with another drive when it filled. The new drive was formatted with the FAT32 filesystem. I had forgotten that the maximum size of a file that can be stored on a FAT32 partition is 4 GB. The Wikipedia File Allocation Article states that it is acutally 4 GB - 2 bytes, i.e. 232 -2 bytes. Microsoft's NTFS filesystem, which is a newer filesystem than FAT32, does not have that limitation. NTFS can support partition sizes exceeding 2 TB.You can use the convert command to convert a FAT32-formatted partition to NTFS.


  1. Backing Up Exchange Information Store
    MoonPoint Support
    October 30, 2006
  2. File Allocation Table
    Wikipedia, the free encyclopedia
  3. NTFS
    Wikipedia, the free encyclopedia