the first time I ran it, it took 2:21mins to write the file, this time it was quicker

srs:/home/icepick# time dd if=/dev/zero of=./testfile bs=65536 count=65536
65536+0 records in
65536+0 records out
4294967296 bytes (4.3 GB) copied, 35.6096 s, 121 MB/s

real 0m35.614s
user 0m0.030s
sys 0m7.850s
srs:/home/icepick# time dd if=./testfile of=/dev/null bs=65536 count=65536
65536+0 records in
65536+0 records out
4294967296 bytes (4.3 GB) copied, 42.8676 s, 100 MB/s

real 0m42.872s
user 0m0.010s
sys 0m0.690s
srs:/home/icepick#