A back end 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 back end is forcibly exported as a single-slice disk.
This option is useful when you want to export the raw content of a back end. For example, if you have a ZFS or Solaris Volume Manager volume where you have already stored data and you want your guest domain to access this data, then you should export the ZFS or Solaris Volume Manager volume using the slice option.
For more information about this option, see Virtual Disk Back End.