Xenserver: you have reached the maximum number of virtual disks allowed for this virtual machine

You have a problem can not add more than 3 vhd to VM windows on XenServer ,it return this error :
you have reached the maximum number of virtual disks allowed for this virtual machine check your settings and try again

Para poder añadir más de 2 discos duros a una virtual machine de Xen Server, solo tienes que instalar las Xenserver tools en el cliente y luego en el gestor activar el/los discos que necesites.