What is the recommended number of replicas in the TiKV cluster? Is it better to keep the minimum number for high availability?

3 replicas for each Region is sufficient for a testing environment. However, you should never operate a TiKV cluster with under 3 nodes in a production scenario. Depending on infrastructure, workload, and resiliency needs, you may wish to increase this number. It is worth noting that the higher the copy, the lower the performance, but the higher the security.