A checkpoint is a snapshot of your search cluster that is stored in the cluster folder (for example, C:\bea\alui\cluster), a shared repository available to all nodes in the cluster. When initializing a new cluster node, or recovering from a catastrophic node failure, the last known good checkpoint will provide the initial index data for the node's partition and any transaction data added since the checkpoint was written will be replayed to bring the node up to date with the rest of the cluster.
Since checkpoint data is of significant size, limit the number of checkpoints maintained by the system. Specify how many checkpoints to keep on the Settings page of the Search Cluster Manager.