File 1,

1141286452,ServerA,Disk Full,Arb data,other,stuff
1141286737,ServerB,Net Down,Arb data,other,stuff
1141286737,ServerC,Disk Full,Arb data,other,stuff

File2,

1141286737,ServerB,Net Down
1141286780,ServerD,Bit Bucket Missing

##</code><code>##

File 1,

1141286452,ServerA,Disk Full
1141286737,ServerB,Net Down
1141286737,ServerC,Disk Full

File2,

1141286737,ServerB,Net Down
1141286780,ServerD,Bit Bucket Missing

##</code><code>##

my %index;
foreach my $entry (@file1) {
    if (not exists $index{$entry}) {
        $index{$entry} = 1
    }
}

foreach my $entry (@file2) {
    if (not exists $index{$entry}) {
        $index{$entry} = 2
    }
    else {
        $index{$entry} += 2;
    }
}

foreach my $entry (keys %index) {
    if ($index{$entry} == 1) {
        print "Entry $entry is only in file one\n";
    }
    elsif ($index{$entry} == 2) {
        print "Entry $entry is only in file two\n";
    }
    elsif ($index{$entry} == 3) {
        print "Entry $entry is in both files\n";
    }
    else {
        print "Entry $entry is screwed up!\n";
    }
}