librenms-librenms/includes/polling/mempools/hrstorage.inc.php

<?php

/// HOST-RESOURCES-MIB - Memory Objects

if (!is_array($storage_cache['hrstorage']))
{
  $storage_cache['hrstorage'] = snmpwalk_cache_oid($device, "hrStorageEntry", NULL, "HOST-RESOURCES-MIB:HOST-RESOURCES-TYPES");
  if ($debug) { print_r($storage_cache); }
}
else
{
  if ($debug) { echo("Cached!"); }
}

$entry = $storage_cache['hrstorage'][$mempool[mempool_index]];

$mempool['units'] = $entry['hrStorageAllocationUnits'];
$mempool['used'] = $entry['hrStorageUsed'] * $mempool['units'];
$mempool['total'] = $entry['hrStorageSize'] * $mempool['units'];
$mempool['free'] = $mempool['total'] - $mempool['used'];

?>