We do it on all our customer HA boxes and our Magento MicroCloudTM/ configurations, so that the fail over system(s) isn't idle. Look into DRBD, Linux VServer and heartbeat. 

Read the following for an insight into it.

http://linux-vserver.org/Getting_high_with_lenny

Caveat
But as always, we advise not trying to do this unless you have substantial experience, as you are more likely to end up with a more unreliable configuration, that is harder to debug and if you end up in a split brain situation, more likely to have data loss ... than a plain old single server.

2 servers, high availability and faster response
Can we make something like chip reader, which can understand chip design and generate blueprint of it?
