How can I speed this function up?

[DarkBlue]

Just to show how much a system set up
impacts these results:
Result from suse10.1 64 , python 2.4 
with AMD FX-55 cpu and about 12 active apps
running in the background. 7200rpm sata drives.

Preparing data...
[write_data1] Preparing output file...
[write_data1] Writing...
[write_data1] Done in 5.43 seconds.
[write_data4] Preparing output file...
[write_data4] Writing...
[write_data4] Done in 4.41 seconds.
[write_data_flush] Preparing output file...
[write_data_flush] Writing...
[write_data_flush] Done in 5.41 seconds.
[write_data_per_line] Preparing output file...
[write_data_per_line] Writing...
[write_data_per_line] Done in 4.4 seconds.
[write_data_once] Preparing output file...
[write_data_once] Writing...
[write_data_once] Done in 4.28 seconds.