While I am annoyed at the presentation of your question, it gave me a chance to abuse $/ in an entertaining fashion. I think I'm either thinking more perly, or going insane. :)

use strict;
open LOG, "C:/fs.log";
$/="\n\n";
while(<LOG>){
    m |^(\w+)\n|; print "Machine $1\n";
    while (m|\n(/.*?\s).*?(\d+)%|gi) {
        print "\t",$2 > 88? "WARNING --> ":"","$1 at $2 %\n"
    }
}
[download]

does the undef need to be there?
Update No, it can be replaced by the "" you see in the ?: .