Clumsy pseudo-pseudo-code... from one who doesn't work with clusters... nor have any ken of their peculiarities, but could something like this conceivably work?

# monitor disk space in a cluster

# create @list_machines -- which do you need to check

my $i = 0; # create counter (flag)

for $_(@list machines) {
    my $machine = $_;   # select machine  # This and the next line == 
+the WEAK POINTS?
    # log in/open $machine 
    # if necessary, my @dirs = selection of dirs to check for change
    my $dir (@dirs) {
        readdir the  dirs in preceding line;         # dir /as for win
+  to obtain dir of all files in all subdirs 
        write dir results to local RAM file, $dir.$machine.$i
        $i++;
        if ( $i == 2 ) { 
            $i = 0; 
        }
        next;
    }
}

sleep (some amount of time);

for $_(@list machines) {
    my $machine = $_;   # select machine  
    if ( (exists $dir.$machine.0) && (exists $dir.$machine.1) ) {
        compare those two files (diff, df, pure-perl list comparison)
        ...PROFIT...
    }
}
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