As pointed out inhttp://email@example.com backup tools (i.e. pg_basebackup, pg_dump[all]), currently don'tmake any efforts to ensure their output is durable.
I think for backup tools of possibly critical data, that's pretty muchunaceptable.
There's cases where we can't ensure durability (i.e. pg_dump | gzip >file), but it's out of our hands in that case.