If you want to copy the hard files from the data/index directory, yes, you'll probably want to shut down the server first. You may be able to get away with leaving the server up but stopping any index/commit operations, but I could be wrong.
How do I stop remote clients to do index/commit operations?
Then, I think, the only solution is to retrieve all documents from the Solr server via an all-matching query and store the search result into some files on hard disk. This should not get in conflict with other clients since it is a normal "user operation", right? If this operation would take several minutes: can other clients still perform queries on the server or even do updates (which should be delayed for consistency)? Or do they get some kind of error messages (a "No server response" would be bad..)?
