Here's the same thing, but with a single regular expression pattern...

while (<DATA>) {
    next unless m{
      ^
      ( aixFsMountPoint | aixFsSize | aixFsFree ) # $1
        \.
      ( \d+                                     ) # $2
        \s* = \s*
      ( .*                                      ) # $3
    }ix;

    $data{$1}{$2} = $3;
}
[download]

But there are plenty of excellent config file (INI file) modules on CPAN for doing this work.

Also, beware the use of the i modifier to match case-insensitively tokens you're then going to use as the keys of a hash.

aixFsMountPoint ≠ aixfsmountpoint ≠ AIXFSMOUNTPOINT