If I understand your question correctly, you are trying to put the device data into a file format that would be easy to load into a perl data structure, like a hash of hashes.

You could read an XML config file with XML::Simple. I think that would be more readable and maintainable than using Data::Dumper.

For example:

<config>
    <drive name="C" used_oid="1.2.3.4.5.1" size_oid="1.2.3.4.6.1"/>
    <drive name="D" used_oid="1.2.3.4.5.3" size_oid="1.2.3.4.6.3"/>
    <drive name="E" used_oid="1.2.3.4.5.3" size_oid="1.2.3.4.6.3"/>
</config>
[download]

Then pull it in using:

use strict;
use XML::Simple;
my $config = XMLin("www.xml");
my $drivename = "C";
print $config->{drive}->{$drivename}->{used_oid},"\n";
[download]

Update: Added an initial problem restatement.