In the current build of DayZ, logs are split with a saw, to craft planks.
Each plank is actually the size of a 2x8x2 board, if not slightly larger.
Sawing a log like this will take a long time, and for the rough shape of the boards anyway, it would make more sense to split them where you need them with an axe tool. Taking less time, and resources.
Sawing any wood with any dimensions using a handsaw is something that takes knowledge of skill, and control.
Even knowing how to do everything right, you can still get to a point where you bind your blade up, or halfway through your cut, realize that you were off from your mark.
Sawing a large log like this into 4 planks would easily totally dull your saw, even with a very well made hand saw.
If you actually had to complete this task in real life, you wouldn't use the saw, you would use an axe to split the wood into these rough planks, maybe planing them or sanding them after if you wanted a smoother surface.