Converting a drive's file system to NTFS
Drives that are formatted with a FAT file system are limited to storing files that are no greater than 4GB in size. If you are backing up to a drive formatted with a FAT file system (external USB hard drive, local drive) and are attempting to backup over 4GB worth of data, the backup will fail and you may see the following error in your backup report:
End of Media encountered while backing up to non-removable media.
To overcome this limitation you can convert your backup disks to the NTFS file system. NTFS does not have the 4GB file size limitation.
More details on NTFS vs FAT
To upgrade a file system from FAT to NTFS without formatting the drive: