Is O_DIRECT_NO_FSYNC safe on FreeBSD with ZFS for MySQL data?

per our understanding, O_DIRECT on freebsd doesn't suffer from the problems that it does on linux. Disabling fsync, however, is likely to be unsafe.
 
Aren't there some ZFS "special" vdevs that are designed for synch writes on a zpool? basically synch writes get to a log first then to zpool so that if the transaction does not complete to the zpool it can be replayed from the special? ZIL and SLOG come to mind as acronyms.
 
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