We had the same problem as someone described in http://mail-archives.apache.org/mod_mbox/lucene-solr-user/201001.mbox/%3c222A518D-DDF5-4FC8-A02A-74D4F232B339@snooth.com%3e. A partial copy of that message:
We're using the new replication and it's working pretty well. There's
one detail I'd like to get some more information about.
As the replication works, it creates versions of the index in the data
directory. Originally we had index/, but now there are dated versions
such as index.20100127044500/, which are the replicated versions.
Each copy is sized in the vicinity of 65G. With our current hard drive
it's fine to have two around, but 3 gets a little dicey. Sometimes
we're finding that the replication doesn't always clean up after
itself. I would like to understand this better, or to not have this
happen. It could be a configuration issue.