The in-tank fuel pump will only produce around 3 bar pressure (I think)... anyway, it's a lot less than what's produced by the high-pressure (mechanical) pump, which typically runs between 250 and 1000 bar. The 2.1 bar reading that you are seeing is coming from the pressure sensor mounted on the fuel rail (ie the high pressure circuit). This is the minimum reading that this sensor will produce; it will read 2.1bar even when there is no pressure at all, and will not register anything in relation to the operation of the in-tank pump.
When cranking the engine, the indicated pressure in the fuel rail should exceed 250 bar within a few seconds.
To test if the in-tank pump is working, either crack off the bleed nipple on top of the filter, or disconnect one of the pipes from the filter and then turn the ignition on (get ready for diesel spillage!). If you disconnect the outlet pipe from the filter, you can attach a length of fuel hose to the filter stub, and collect the diesel in a suitable container (this will also allow you to visually examine the state of the fuel being delivered, as well as verifying that the filter is flowing OK). You could also attach a low pressure guage to this outlet to confirm that the in-tank pump is producing enough pressure.
The fuel injectors will not be triggered until a pressure threshold in the fuel rail is exceeded (I'm guessing this must be around 200 bar). No pressure in fuel rail = no injector pulse. I have had a jtd non-starter once which was caused by failure of the pressure sender, which would only ever show 2.1 bar; even though the high pressure pump was working correctly, the ecu would not trigger the injectors.
A word of warning: when working correctly, the pressure produced in the fuel rail and associated pipework etc is extremely high (up to 1000bar) and potentially very dangerous! Be very careful!