I know the probability of this is very low, but I have a 250G hard drive that I just reformatted and re-installed the OS on (centos, ext3). It turns out there was one large file (a 20G xen image) on that disk that we should have saved. The hard drive was about 80% full before the install, and now it only has about 10G written to it, so in all probability the actual sectors the file used to reside on were not overwritten by the install process (though the format may have cleaned everything out)
Is there any chance of recovering that file? Or did the format / reinstall wipe out all residual traces of it?