Ginger graters are made from ceramic or porcelain, or less commonly, carved from bamboo.
Ginger is very hard to grate: many recommend not even to bother trying and to just mince it instead.
For those who aren’t so easily dissuaded, the problem you will face is how fibrous ginger is.
If you get to pick the piece of ginger you have to work with, you’ll find that younger ginger (with smooth, thin skin) is less fibrous. Failing that, try freezing the ginger first, and grating it while frozen (in fact, the freezer is an ideal place to store whole pieces of ginger.)
When you first start grating a piece of ginger, you’ll get a reasonable amount of grated flesh, but then you run into a wall, when you’ve removed the flesh and are working on just fibre. Take a second to slice the fibres off, and start grating again.
Some try to use a garlic press on ginger, but it will yield you only ginger juice.