Choose what the backup must preserve
A full DVD backup and a portable movie file solve different problems. Use a folder or ISO when menus, title layout, chapters, extras, and original streams matter. Use MKV when selected titles and multiple tracks matter more than disc navigation. Use MP4 when broad device playback and smaller files are the priority.
Plan storage and file names
Estimate space before starting and use a consistent folder and filename convention for films, seasons, discs, and bonus material. Keep at least one verified copy on storage separate from the working computer. A backup on the same failing drive is not an independent backup.
Preserve source properties
DVD video can be interlaced and can rely on display-aspect metadata. Preserve frame rate, field order, and aspect ratio unless the destination requires an intentional change. Select the correct audio and subtitle languages before processing.
Test restoration, not only creation
Mount or open the output and play more than the first minute. Check title order, chapter access, picture, audio, subtitles, and sync. A backup is useful only when the intended player or editor can read it reliably.