diff --git a/lib/vmpooler/vsphere_helper.rb b/lib/vmpooler/vsphere_helper.rb
index 1d44af2..622b66d 100644
--- a/lib/vmpooler/vsphere_helper.rb
+++ b/lib/vmpooler/vsphere_helper.rb
@@ -2,6 +2,10 @@ require 'rubygems' unless defined?(Gem)
 
 module Vmpooler
   class VsphereHelper
+    ADAPTER_TYPE = 'lsiLogic'
+    DISK_TYPE = 'thin'
+    DISK_MODE = 'persistent'
+
     def initialize(_vInfo = {})
       config_file = File.expand_path('vmpooler.yaml')
       vsphere = YAML.load_file(config_file)[:vsphere]
@@ -12,6 +16,60 @@ module Vmpooler
                                          insecure: true
     end
 
+    def add_disk(vm, size, datastore)
+      begin
+        @connection.serviceInstance.CurrentTime
+      rescue
+        initialize
+      end
+
+      return false unless size.to_i > 0
+
+      vmdk_datastore = find_datastore(datastore)
+      vmdk_file_name = "#{vm['name']}/#{vm['name']}_#{find_vmdks(vm['name'], datastore).length + 1}.vmdk"
+
+      controller = find_disk_controller(vm)
+
+      vmdk_spec = RbVmomi::VIM::FileBackedVirtualDiskSpec(
+        capacityKb: size.to_i * 1024 * 1024,
+        adapterType: ADAPTER_TYPE,
+        diskType: DISK_TYPE
+      )
+
+      vmdk_backing = RbVmomi::VIM::VirtualDiskFlatVer2BackingInfo(
+        datastore: vmdk_datastore,
+        diskMode: DISK_MODE,
+        fileName: "[#{vmdk_datastore.name}] #{vmdk_file_name}"
+      )
+
+      device = RbVmomi::VIM::VirtualDisk(
+        backing: vmdk_backing,
+        capacityInKB: size.to_i * 1024 * 1024,
+        controllerKey: controller.key,
+        key: -1,
+        unitNumber: find_disk_unit_number(vm, controller)
+      )
+
+      device_config_spec = RbVmomi::VIM::VirtualDeviceConfigSpec(
+        device: device,
+        operation: RbVmomi::VIM::VirtualDeviceConfigSpecOperation('add')
+      )
+
+      vm_config_spec = RbVmomi::VIM::VirtualMachineConfigSpec(
+        deviceChange: [device_config_spec]
+      )
+
+      @connection.serviceContent.virtualDiskManager.CreateVirtualDisk_Task(
+        datacenter: @connection.serviceInstance.find_datacenter,
+        name: "[#{vmdk_datastore.name}] #{vmdk_file_name}",
+        spec: vmdk_spec
+      ).wait_for_completion
+
+      vm.ReconfigVM_Task(spec: vm_config_spec).wait_for_completion
+
+      true
+    end
+
     def find_datastore(datastorename)
       begin
         @connection.serviceInstance.CurrentTime
@@ -23,6 +81,99 @@ module Vmpooler
       datacenter.find_datastore(datastorename)
     end
 
+    def find_device(vm, deviceName)
+      begin
+        @connection.serviceInstance.CurrentTime
+      rescue
+        initialize
+      end
+
+      vm.config.hardware.device.each do |device|
+        return device if device.deviceInfo.label == deviceName
+      end
+
+      nil
+    end
+
+    def find_disk_controller(vm)
+      begin
+        @connection.serviceInstance.CurrentTime
+      rescue
+        initialize
+      end
+
+      devices = find_disk_devices(vm)
+
+      devices.keys.sort.each do |device|
+        if devices[device]['children'].length < 15
+          return find_device(vm, devices[device]['device'].deviceInfo.label)
+        end
+      end
+
+      nil
+    end
+
+    def find_disk_devices(vm)
+      begin
+        @connection.serviceInstance.CurrentTime
+      rescue
+        initialize
+      end
+
+      devices = {}
+
+      vm.config.hardware.device.each do |device|
+        if device.is_a? RbVmomi::VIM::VirtualSCSIController
+          if devices[device.controllerKey].nil?
+            devices[device.key] = {}
+            devices[device.key]['children'] = []
+          end
+
+          devices[device.key]['device'] = device
+        end
+
+        if device.is_a? RbVmomi::VIM::VirtualDisk
+          if devices[device.controllerKey].nil?
+            devices[device.controllerKey] = {}
+            devices[device.controllerKey]['children'] = []
+          end
+
+          devices[device.controllerKey]['children'].push(device)
+        end
+      end
+
+      devices
+    end
+
+    def find_disk_unit_number(vm, controller)
+      begin
+        @connection.serviceInstance.CurrentTime
+      rescue
+        initialize
+      end
+
+      used_unit_numbers = []
+      available_unit_numbers = []
+
+      devices = find_disk_devices(vm)
+
+      devices.keys.sort.each do |c|
+        next unless controller.key == devices[c]['device'].key
+        used_unit_numbers.push(devices[c]['device'].scsiCtlrUnitNumber)
+        devices[c]['children'].each do |disk|
+          used_unit_numbers.push(disk.unitNumber)
+        end
+      end
+
+      (0..15).each do |scsi_id|
+        if used_unit_numbers.grep(scsi_id).length <= 0
+          available_unit_numbers.push(scsi_id)
+        end
+      end
+
+      available_unit_numbers.sort[0]
+    end
+
     def find_folder(foldername)
       begin
         @connection.serviceInstance.CurrentTime
@@ -169,6 +320,29 @@ module Vmpooler
       vms
     end
 
+    def find_vmdks(vmname, datastore)
+      begin
+        connection.serviceInstance.CurrentTime
+      rescue
+        initialize
+      end
+
+      disks = []
+
+      vmdk_datastore = find_datastore(datastore)
+
+      vm_files = vmdk_datastore._connection.serviceContent.propertyCollector.collectMultiple vmdk_datastore.vm, 'layoutEx.file'
+      vm_files.keys.each do |f|
+        vm_files[f]['layoutEx.file'].each do |l|
+          if l.name.match(/^\[#{vmdk_datastore.name}\] #{vmname}\/#{vmname}_([0-9]+).vmdk/)
+            disks.push(l)
+          end
+        end
+      end
+
+      disks
+    end
+
     def get_base_vm_container_from(connection)
       begin
         connection.serviceInstance.CurrentTime