Small Redundant web/mail setup

[Ian Lord]

Hi,

I need to setup a high-availability setup for mail/web setup

I was thinking about the following setup:

4 servers total:

Data Servers:
         1 Server holding all the websites data and mail messages. It 
would serve these files via nfs to the application servers.
         It would also run mysql

         A second server Also sharing it's content via nfs, 
replicating it's data though rsync each ?? minutes. The mysql would 
run as a slave of the    primary

Application Servers:
         Both servers would be running apache, php, sendmail and 
posfix and would serve content from the share nfs drive.

1- Is this a viable solution, I mean by that, Is it Like this big ISP 
are set up ?

2- Is there a better way to replicate data than RSYNC (without going 
to san of expensive hardware) ? If not, is there a hotsync feature (I 
mean by that as soon as server A modify something, server B knows and 
replicate)?

I would appreciate if you could give me feedbacks, suggestions, or if 
you see any problem that might happen with this kind of setup.

Thanks a lot