This isn't addressing your question, but one thing I noticed in your code is your verbose method of initializing %data. Note:
use Test::More;
use constant MY_KEYS =>
qw( rrqms wrqms reads writes rsecs wsecs avgrqsz avgqusz await svctm
+ util );
my $key = 'asdf';
my @list = ( 'a' .. 'l' );
my %data;
(
undef, $data{io}{$key}{rrqms},
$data{io}{$key}{wrqms}, $data{io}{$key}{reads},
$data{io}{$key}{writes}, $data{io}{$key}{rsecs},
$data{io}{$key}{wsecs}, $data{io}{$key}{avgrqsz},
$data{io}{$key}{avgqusz}, $data{io}{$key}{await},
$data{io}{$key}{svctm}, $data{io}{$key}{util}
) = @list;
my %data2;
( undef, @{ $data2{io}{$key} }{ +MY_KEYS } ) = @list;
my %data3;
@{ $data3{io}{$key} }{ +MY_KEYS } = @list[ 1 .. $#list ];
is_deeply \%data, \%data2, "Assigning an array to a slice.";
is_deeply \%data, \%data3, "Assigning a slice to a slice.";
done_testing();
__END__
__OUTPUT__
ok 1 - Assigning an array to a slice.
ok 2 - Assigning a slice to a slice.
1..2