instead of processing the elements of the array one after each other, i create a list out of the elements. then a mod-3 counter puts them in the appropriate slot - that is the (IMO) cool part distinguishing the solution from the one leriksen gave.

use strict;
use Data::Dumper;

my @array = ('nfs,7,rw',
             'afp,12,rro',
             'cifs,32,ro',
             'dns,5,rw',
);

my @splitted_up = ();
my $cnt = 0;
push @{ $splitted_up[($cnt ++) % 3] }, $_ 
   foreach (split (/,/, join (",",@array)));
print (Dumper \@splitted_up);
[download]

generated output is the same.