On another 3d I was asking about a simple solution to create a single file that will fill up completely the free space of a given disk writing all bits to 1. Someone has suggested to write the following command line on terminal: tr '\000' '\3ff' < /dev/zero | dd of=zero.bin bs=1k count=10 The problem is that it is working on Linux but in Mac OS X (SL) his output is not all '1'.. does anyone know a solution? And that's not all.. in fact I'd like to write this file in blocks of 4k, not 1K.. is it enough to change bs=1k to bs=4k? what about the tr command in such case? Well, my only aim is to fill up the free space with all bits written to 1, if some of you know a better solution or find easier to write a simple program.. everything is welcome!