strange gigabit

hello,


a)
if i copy a file from local to a samba share => 1 Mo / secs

before the first copy end,
if i copy another file => the 2 rates jump to 30 Mo / secs


b)
if i copy from samba share to local => 30Mo / secs


i don't understand why the read from the share is ok
and why i had to copy 2 files to the share to get the same rate ???


my conf :

2 gigabit controller :
- 1 nvidia ethernet controller
- 1 netgear ethernet controller ( GA311 )

1 gigabit switch netgear GS605

samba3

distro : mandriva 2006

same pb with kernel 2.6.12 -> 2.6.16


any idea ?