very slow insert, very large iowait

[Jean-Paul Le Fèvre]

I'm working with a big table (~20 millions row, 2 Gbytes)
and which will likely get bigger. There are indexes on the
columns. I've the impression that something is wrong when
I carry out massive insertions. The server is running on
a 4 CPU linux machine with 2 Gbytes of RAM.

Running top(1) I see that less than 10% of the CPU,
about 40% of the memory are used but that iowait is
always more than 240% (> 2 * 95% + 2 * 25%)

I don't know if I can get rid of this bottleneck.
My parameters are the following :

skip-locking
key_buffer_size = 512M
table_cache = 256
max_allowed_packet = 16M
sort_buffer_size = 128M
net_buffer_length = 8K
read_buffer_size = 1M
read_rnd_buffer_size = 8M
myisam_sort_buffer_size = 64M
bulk_insert_buffer_size = 64M
query_cache_size = 16M
preload_buffer_size = 16M
thread_cache = 8
thread_concurrency = 4