Flush buffers to disk
H5F.flush(object_id,scope) causes all buffers
associated with a file to be immediately flushed to disk without removing
the data from the cache.
object_id can be any object
associated with the file, including the file itself, a dataset, a
group, an attribute, or a named data type.
whether the scope of the flushing action is global or local.
be one of the following strings: