The latest engine version of Amazon ElastiCache for Redis now comes with several enhancements:

• More usable memory: You can now safely allocate more memory for your application without the risk of increased swap usage during syncs and snapshots.
• Improved synchronization: Improved output buffer management provides more robust synchronization under heavy load and when recovering from network disconnections. Additionally, syncs are faster as both the primary and replicas no longer use the disk for this operation.
• Smoother failovers: In the event of a failover, your cluster now recovers faster as replicas will avoid flushing their data to do a full re-sync with the primary.

Source: Amazon Web Services News