file_column and nfs shared

Hi,

I use file_column (0.3.1) for image and mp3 uploads. Data are
shared among 4 application servers using NFS. Web servers
is Mongrel with 20 processes per server.

But it doesn't scale well as I got this error:

A Errno::ENOENT occurred in user#update_detail:

No such file or directory -
/home/rails/current/config/../public/user/image/tmp/1158426179.333537.17133
or /home/rails/current/config/../public/user/image/846
/usr/lib/ruby/1.8/fileutils.rb:500:in `rename'

Is it a thread problem ? Lock error ? NFS is too slow ?

Any ideas ?
Help is very, very welcome...
Thanks in advance
Seb