&quot;One of the goals of such systems is that copy of the file system on disk is always consistent.&quot;<p>Goal yes, implementation no.  WAFL does in fact have consistency problems and filers do ship with a consistency checker called &quot;wack&quot; which if you ever need this tool you&#x27;ll probably have better luck throwing the filer in the trash and restoring from backups rather than waiting a month for it to complete.