XFS implements an optimization to sync(2) of metadata:
XFS will only force the log out, such that any dirty metadata that is incore is written to the log only, the metadata itself is not necessarily written
This is safe, since all change is ondisk
File data is guaranteed too (even barriers)
Log and metadata are written to disk for
freeze/thaw
remount ro
unmount
Applications like grub have been bitten in the past, but fixed nowadays
