Hello,
You should have a look at these notes :
Note 361123 - SAP content server and security
Note 1039401 - SAP Content Server Clustering with Windows 2003.
The note 361123 points out the following document about HA for content server :
http://service.sap.com/ContentServer
in the section "Media Library > > Literature > > High Availability.pdf".
These are about Windows but the idea is to get inspired by these notes and get it set up in your environment. This should not be much complicated as basically it is all about clustering the web server and a file system or a database depending on the type of content server storage you choose ( flie system or max db ) .
Best regards,
Steve.