Is this what you want?

use strict;
use warnings;
[download]

my %usage;
my @files = qw(sfull1ns.dat sfull2ns.dat sfull3ns.dat);

for my $file ( @files ) {

    open( my $fh, "<", $file ) or die "Can't open file $file: $!";

    <$fh>; # Skip header line
    
    while ( my $line = <$fh> ) {
        chomp($line);

        my ( $server, @data ) = ( split( ",", $line ) );

        $usage{$server}{$file}{value} ||= $data[0];
    }
}

for my $file (@files) {
    $usage{$_}{$file}{value} ||= 0 for keys %usage;
}

for my $server (sort keys %usage) {
    print "$server,",
        join (',', map {$usage{$server}{$_}{value}} sort keys %{$usage
+{$server}}),
        "\n";
}
[download]