Solr crawls during replication

[Mark]

We have an index around 25-30G w/ 1 master and 5 slaves. We perform 
replication every 30 mins. During replication the disk I/O obviously 
shoots up on the slaves to the point where all requests routed to that 
slave take a really long time... sometimes to the point of timing out.

Is there any logical or physical changes we could make to our 
architecture to overcome this problem?

Thanks