You were using the same variable $x for max and min, and never updating it, nor comparing with the current max value for a $server and $metric combination. I'm surprised either max or min was correct. I suggest an alternative approach.

while(<DATA>){
    next unless /\w/;
    my($server,$datetime,$metric,$value) = (split)[0,1,2,3];
    $value =~ s/,//g ;
    my $ddhh = substr $datetime,0,13;
    my $dd   = substr $datetime,0,10;
    if (! defined($d{$dd    }{$server}{$metric}{max})) {
      $d{$dd    }{$server}{$metric}{max} = 0; 
      $d{$dd    }{$server}{$metric}{min} = 99999999;
      $h{$ddhh  }{$server}{$metric}{max} = 0;
      $h{$ddhh  }{$server}{$metric}{min} = 99999999;
    }
    $d{$dd    }{$server}{$metric}{max} = $value if ($d{$dd    }{$serve
+r}{$metric}{max} < $value);
    $d{$dd    }{$server}{$metric}{min} = $value if ($d{$dd    }{$serve
+r}{$metric}{min} > $value);
    $h{$ddhh  }{$server}{$metric}{max} = $value if ($h{$ddhh  }{$serve
+r}{$metric}{max} < $value);
    $h{$ddhh  }{$server}{$metric}{min} = $value if ($h{$ddhh  }{$serve
+r}{$metric}{min} > $value);
    $ser{$server} = 1;
    $met{$metric} = 1;
}
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