To reduce the reindex time for a large index, consider the following strategies: 1. Increase the number of shards: Distribute the index across more shards to parallelize the reindexing process. 2. Use a faster storage: Ensure that the storage system used for the index is optimized for speed, such as using SSDs instead of HDDs. 3. Optimize the source index: Remove unnecessary fields and reduce the size of documents in the source index to speed up the reindexing process. 4. Use bulk requests: Reindex data in bulk to reduce the overhead of individual requests. 5. Adjust the refresh interval: Temporarily increase the refresh interval of the target index to reduce the overhead of frequent refreshes during reindexing. 6. Throttle the reindexing process: Use the `requests_per_second` parameter to control the rate of reindexing and prevent overwhelming the cluster. 7. Use parallel reindexing: If possible, run multiple reindexing tasks in parallel to speed up the process. 8. Monitor and optimize cluster performance: Ensure that the cluster is not overloaded and has sufficient resources to handle the reindexing task efficiently.