# 1 GB:
$ time dd if=/dev/zero of=test.dat bs=512 seek=2097152 count=1
1+0 records in
1+0 records out
512 bytes transferred in 0.019545 secs (26196 bytes/sec)

real	0m9.117s
user	0m0.001s
sys	0m0.236s

# 10 GB:
$ time dd if=/dev/zero of=test.dat bs=512 seek=20971520 count=1
1+0 records in
1+0 records out
512 bytes transferred in 0.000022 secs (23342214 bytes/sec)

real	1m25.401s
user	0m0.001s
sys	0m2.316s