BTW, David, test (if you have enough time for curiosity) /dev/
urandom (or
wherever the generator is) with different values of 'bs', from very
small to large (1 byte, 512, 4k, 16k, 64k) to see how much it depends
on block size.
bash-2.05b$ time dd if=/dev/urandom bs=1024 count=10240 of=/dev/null
10240+0 records in
10240+0 records out
10485760 bytes transferred in 0.154649 secs (67803598 bytes/sec)
~% cat test_rand_block.sh
#!/usr/local/bin/bash
for BS in 1 512 $(expr 1024 \* 4) $(expr 1024 \* 16) $(expr 1024 \*
64); do
COUNT=$(expr $(expr 1024 \* 64) / $BS)
BYTES=$(expr $COUNT \* $BS)
echo bs=$BS count=$COUNT bytes=$BYTES
dd if=/dev/random of=/dev/null bs=$BS count=$COUNT
echo ------;
done
~% sh test_rand_block.sh
bs=1 count=65536 bytes=65536
65536+0 records in
65536+0 records out
65536 bytes transferred in 25.599306 secs (2560 bytes/sec)
------
bs=512 count=128 bytes=65536
128+0 records in
128+0 records out
65536 bytes transferred in 0.099902 secs (656003 bytes/sec)
------
bs=4096 count=16 bytes=65536
16+0 records in
16+0 records out
65536 bytes transferred in 0.100660 secs (651062 bytes/sec)
------
bs=16384 count=4 bytes=65536
4+0 records in
4+0 records out
65536 bytes transferred in 0.099324 secs (659820 bytes/sec)
------
bs=65536 count=1 bytes=65536
1+0 records in
1+0 records out
65536 bytes transferred in 0.099681 secs (657458 bytes/sec)
------
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