I guess you might need following output:

host1:
vol1: 10g
vol2: 20g
vol3: 30g
total:60h

host2:
vol4:30g
vol5:20g
vol2:20g
total:70g

You should have data structure:

 $VOLUMES = { vol1 => '10' , vol2 => '20', ... };
 $HOSTS  = { host1 => [qw(vol1 vol2 vol3),
                host2 => [qw(vol4 vol5 vol2)], ... };
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Iterate each host from $HOSTS (in sorted order) and iterate for each volume and get the values from other hash. and total them for capacity. </code>