No, not a good idea.

This will use all the bit patterns between 100_0001 and 101_0101. Of interest is that the upper 3 bit are always set to 010. This flaw might be sufficient to allow a sufficiently motivated person to extract something useful.

This would be better written as

    1 while print F chr(rand(256));
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As an added bonus, when the file system is full, the print wil fail, the call will return 0 and bingo! you fall out of the while. At least I believe that that is what should happen. You'll forgive me if I don't try this out on my own filesystem...