clickhouse 文档里的划分冷热多盘存储配置真的是按时间划分冷热数据的吗？

https://clickhouse.com/docs/en/engines/table-engines/mergetree-family/mergetree/#table_engine-mergetree-multiple-volumes

move_factor：when the amount of available space gets lower than this factor, data automatically starts to move on the next volume if any (by default, 0.1). ClickHouse sorts existing parts by size from largest to smallest (in descending order) and selects parts with the total size that is sufficient to meet the move_factor condition. If the total size of all parts is insufficient, all parts will be moved.

看文档的解释，应该是按 part 的大小优先把大的 part 移到下一个盘

但是什么样的数据会被合并成一个 part 的呢？

大的 part 一定就是时间久远的数据吗？