mkfile utility, like on Solaris.

mkfile.py

#!/usr/bin/env python
"""
  A small utility to create a file of specified size:

  $ mkfile 100g
"""
import sys
import time
import os

B = 1
K = 1024
M = K*K
G = K*M

def get_size(s):
  size = int(s[:-1])
  m = s[-1:]
  if m == 'b' or m == 'B':
    return size*B
  elif m == 'k' or m == 'K':
    return size*K
  elif m == 'm' or m == 'M':
    return size*M
  elif m == 'g' or m == 'G':
    return size*G
  else:
    raise Exception('Invalid format: %s' % s)

def mkfile(fname, size, chunk=1024) :
  n_chunks = size // chunk

  bite = bytearray(chunk)
  payload = bytearray(size % chunk)

  with open(fname, "wb") as f:

    for n in range(n_chunks) :
      f.write(bite)

    f.write(payload)
    f.flush()
    os.fsync(f.fileno())


if len(sys.argv) != 3:
  print 'Usage: <file> <size><b|k|m|g>'
  sys.exit(1)

fname = sys.argv[1]
size =  get_size(sys.argv[2])

time_start = time.time()
mkfile(fname, size, 8192)
time_stop = time.time()
delta = time_stop - time_start
print '%.2f MB/s' % (size / M / delta)