time dd if=/dev/urandom of=test.dat bs=2G count=1 iflag=fullblock 1+0 records in 1+0 records out 2147483648 bytes (2,1 GB) copied, 139,519 s, 15,4 MB/s real 2m19.622s user 0m0.000s sys 2m8.581s
time openssl rand -out test.dat -base64 $(( 2*2**30 * 3/4 ))
real 0m25.414s
user 0m24.219s
sys 0m0.882s