how to backup lucene index file

[鞠朕]

Hi,    I am using Lucene to build a Full Text search system, I put the index 
file in some Directory in my server, Considering robust, I think i shouldbackup 
the index file in somewhere else. If the index file is broken, i can switch to 
the backup one.    Can you tell me how to do this, use what API, can you give 
me a simple demo.    Thanks,From juzhen