whether it's RS6000 with JFS, Linux, log-structured file systems or
fossil, unless writes are write-through to disc, if you simply
reset the machine, i'd expect you stand a good chance of losing data
you've written just (ie, instantly) before the reset
(unless the system somehow intercepts the reset).

the systems might use one or more of journalling, soft-writes, or
ordered writes to ensure the logical consistency of the stored file system
data and metadata, if the system is interrupted at arbitrary points.
but nevertheless, unless they buffer all modified data through intermediate NVRAM
that they pick up after a boot, that's just the consistency on storage,
and you'll lose whatever doesn't get to disc before the reset (or if
the device can't write it before power fails).  it might check
cleanly, because the metadata is consistent, but a file is empty!