A range in CockroachDB (called a “shard” in other databases) is a chunk of data, stored as key-value pairs. The Distribution Layer breaks tables apart into these chunks so the data can be distributed across different nodes.
In CockroachDB, a range is 512 MiB or smaller. This default range size is a sweet spot – small enough to move quickly between nodes, but large enough to store a meaningfully contiguous set of data whose keys are more likely to be accessed together. Once a range gets bigger than 512 MiB, it’s split into two smaller chunks in order to keep the ranges from getting too big.