A backend is normally exported either as a full disk or as a single slice disk depending on its type. If the slice option is specified, then the backend is forcibly exported as a single slice disk.
This option is useful when you want to export the raw content of a backend. For example, if you have a ZFS or SVM volume where you have already stored data and you want your guest domain to access this data, then you should export the ZFS or SVM volume using the slice option.
For more information about this option, see Virtual Disk Backend.