how to convert this to C#
See the question and my original answer on StackOverflowYou must use P/Invoke interop to access DeviceIoControl. Here is a link that has similar calls and should be a good starting point: Defrag API C# wrappers
Simon Mourier's blog (1807 answers on StackOverflow) about Microsoft technologies C#, C/C++, .NET, WinRT, WinUI3, AOT, P/Invoke, COM, Interop, DirectX, Direct2D, Windows, ...