ZFS will behave differently on different platforms when given a whole disk.
On illumos, ZFS attempts to enable the write cache on a whole disk. The illumos
(nee Solaris) UFS driver cannot ensure integrity with the write cache enabled, so by default Sun/Solaris systems using UFS file system for boot were shipped with drive write cache disabled (long ago, when Sun was still an independent company). For safety on illumos, if ZFS is not given the whole disk, it could be shared with UFS and thus it is not appropriate for ZFS to enable write cache. In this case, the write cache setting is not changed and will remain as-is. Today, most vendors ship drives with write cache enabled by default.
On Linux, the Linux IO elevator is largely redundant given that ZFS has its own IO elevator, so ZFS will set the IO elevator to noop to avoid unnecessary CPU overhead.