1. A method of simulating a target storage configuration for a computer system, wherein the target storage configuration may comprise multiple storage units, the method comprising: receiving a storage command from an application running on the computer system into a storage protocol stack on the computer system, wherein said storage protocol stack is part of an operating system of the computer system and runs in kernel mode; intercepting the storage command within the storage protocol stack by a kernel simulator module incorporated into the storage protocol stack; forwarding the intercepted storage command from the kernel simulator module to a userland simulator module running in user mode; generating a response to the storage command in the userland simulator module, said response emulating the behaviour of the target storage configuration; sending the generated response from the userland simulator module to the kernel simulator module; and returning the response from the kernel simulator module to the application via the storage protocol stack.