For a FFS on an SSD, which of "-o" nil, "sync" &/ "softdep" is more data-safe and fast?

Hi!

If I understand mount(8) (http://man.openbsd.org/mount) right, FFS
mounts have a metadata I/O mode and a data I/O mode. By default,
metadata is accessed synchronously and data is accessed
asynchronously.

"-o sync" will force both to synchronous mode, and "-o softdep" would
change the metadata I/O mode to the alternative softdep access mode.


What is the optimal sync &/ softdep configuration for minimizing risk
of data loss on unexpected reboot, and maximizing overall filesystem
I/O speed?

By "data loss" I mean in particular filesystem structure issues that
could cause fsck(8) hickups and stability issues (e.g. the "/var/log"
directory disappearing altogether - I've seen that happen), secondarily
that file data content updates not would have stuck on the disk.

Either nothing (no "-o" setting), or "-o sync,softdep", or "-o sync",
would all look like they'd make sense.

(Can you even do "-o sync,softdep", would that serve any purpose?)

Will appreciate to learn your thoughts on this one a lot,

Thanks,
Tinker