using dd to wipe a disk

I know the command

dd if=/dev/urandom of=/dev/hda bs=? count=?

can be used to fill a disk with random bytes and is a good way to clean it
prior to recycling or reselling. However, it is slow due to the random
number generation.

Substituting /dev/zero makes it run around 22 times faster but is not
quite as secure. Which brings me to this question.

If I wanted to iteratively write a series of bytes, could be a pattern, a
small file of random numbers, or whatever, can I modify the command so
that if=filename or if=pattern is used over and over again whenever it's
input buffer is dry and until the disk is full or count reached?

I created a small 1kb random.seed file (much like init does as shutdown),
but all that would be done was 1kb of output.

dd if=my.random.file of=/dev/hda ibs=1K obs=1M count=(a lot for 30gb)
where count would be the number of input file blocks. But it only went
through once.

Or, would the badblocks program be a better substitute?

Feeback and comments appreciated!
--
Peter
.

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