In Redis Cluster, explain how keys are distributed and what happens during a resharding.

Redis Cluster uses 16384 hash slots (CRC16(key) % 16384). Each master owns a slot range. During resharding, slots are migrated one key at a time using CLUSTER SETSLOT, MIGRATE, and CLUSTER COUNTKEYSINSLOT. Clients receive MOVED (permanent redirect) or ASK (migration in progress) redirects.