Ollydbg run traces and in a plain text format. I'm constrained by my target application only working on older versions of windows, so I can't easily insert a compression step in the log generation or switch to a more compact binary representation.

(I'm currently looking into solutions like a custom filesystem driver, running a second VM and using internal networking to stream to a FUSE filesystem, or possibly even hooking the filesystem access of my debugger and inserting a compression step into WriteFile() calls)