A Fusion Drive is not a single physical part but a logical volume managed by macOS.
Because it links two physical drives into one volume, if either component fails, all data on both drives typically becomes unreadable. Purchasing and Replacement Options buy fusion drive
Used in later models like the 2015-2017 iMacs. Available for roughly $17 to $50 at eBay - beetstech or eBay - discountparts99. A Fusion Drive is not a single physical
Standard 3.5-inch or 2.5-inch SATA HDDs can be used as the mechanical component. if either component fails