Re: /dev/random and dd

Whow... After some trouble trying to compile it under libc5  (gave up on that one - 
I'm on RH7.2), I ended up doing a static then strip against my libc6. That required 
a little rming in tomsrtbt...

Anyway. Performance is now much improved, although not yet enough to keep 
the HD busy on the old hardware I'm using. I'm getting about 300k/s, but the HD 
could do probably about 3 times that (tried a few old machines). I guess there will 
be a break-even point, as processors increase in speed much more than bus/hd - 
so it should be OK on newer hardware - but on the stuff I'm running at the 
moment, it's still a little slow.

If a faster version springs to mind, let me know. I'll try and see if I can compile 
GNU's shred for tomsrtbt in the meantime. But I'm _not_ a C programmer (at all), 
so I may not go very far...

Thanks ever so much, help much apreciated.

Yan


----  On 21 May 2002, at 15:32, [email protected] wrote:  ----

> On Tue, 21 May 2002 [email protected] wrote:
> 
> > Am I right then in thinking there's really no easy solution with Linux? (short of 
> > leaving the dd running overnight, or mounting the HD in another (faster) machine...)
> 
> There are kerjillions of easy ways of doing it with Linux :).
> 
> You could write a simple program that uses standard library random
> function for generating random data. That should be way faster than
> /dev/*random as its should have a rather plainforward implementation.
> 
> Then you can direct its output to /dev/hda or use dd if you wish.
> 
> More than 5,6 megabytes under 3 seconds with the following:
> --------------------------------------------------------
> #include <stdlib.h>
> #include <stdio.h>
> #include <errno.h>
> 
> int main(int argc, char *argv[]){
>         int seed;
>         if (argc != 2){
>                 printf ("Usage: %s [seed], "
>                         "where seed can be any integer.\n", argv[0]);
>                 exit (1);
>         }
>         errno=0;
>         if ((seed = atol(argv[1])) && !errno)
>                 srand(seed);
>         else {
>                 printf ("Error: %s: %s\n", argv[1],
>                         errno ? "Numerical result out of range." : "Not a  number.");
>                 exit (2);
>         }
>         while (1) printf("%d",rand());
> }
> 
> Compile it with
> gcc -o rand rand.c
> and strip symbols with
> strip -s rand
> and you'll get a 3kB binary that should fit into tomsrtbt easily.
> 
> Usage:
> rand 12347 | dd of=/dev/hda
> or
> rand 12347 > /dev/hda
> 
> 
> Drop me a note if you need a smaller or faster version -- printf is
> overhead, using library rand() is also overhead. I guess it can be done
> under 1 kB and considerably faster than with stdlib rand(), as the latter
> uses long integers.
> 
> Regards,
> m
> 


-- 
Yan Fitterer
IT Manager, Royal Academy of Music
E-mail : [email protected]
Marylebone Rd, London, NW1 5HT
Phone (+44) 20 7873 7365 Fax (+44) 20 7873 7364