On 2009-Nov-24 14:07:06 -0600, Mike Gerdts <mger...@gmail.com> wrote: >On Tue, Nov 24, 2009 at 1:39 PM, Richard Elling ><richard.ell...@gmail.com> wrote: >> Also, the performance of /dev/*random is not very good. So prestaging >> lots of random data will be particularly challenging.
This depends on the random number generation algorithm used in the kernel. I get >50MB/sec out of FreeBSD on 3.2GHz P4 (using Yarrow). In any case, you don't need crypto-grade random numbers, just data that is different and uncompressible - there are lots of relatively simple RNGs that can deliver this with far greater speed. >I was thinking that a bignum library such as libgmp could be handy to >allow easy bit shifting of large amounts of data. That is, fill a 128 >KB buffer with random data then do bitwise rotations for each >successive use of the buffer. Unless my math is wrong, it should >allow 128 KB of random data to be write 128 GB of data with very >little deduplication or compression. A much larger data set could be >generated with the use of a 128 KB linear feedback shift register... This strikes me as much harder to use than just filling the buffer with 8/32/64-bit random numbers from a linear congruential generator, lagged fibonacci generator, mersenne twister or even random(3) http://en.wikipedia.org/wiki/List_of_random_number_generators -- Peter Jeremy
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