I see a article about a custom memory reservation :
"default reservation of 0MB means the ESX/ESXi host does not have to provide the virtual machine with any physical memory. The virtual machine get its memory with VMkernel swap. VMkernel swap if a file created when a virtual machine is powered on with a .vswp extension. By default, this file will be equal to the size of the RAM that you configured the virtual machine. A virtual machine can get its memory allocation entirely from VMkernel swap – or disk – resulting in virtual machine performance degradation."
So, should it set the the memory reservation value rather than leave it as default, ie 0 ?