A. After a snapshot is deleted, the snapshot data unique to the snapshot will be emptied, and the data at the point in time when the snapshot was created becomes unavailable. However, the data shard dependencies will not change to ensure that the data can be accessed normally according to the dependencies next time.

B. When the snapshot is created, the data layer does not change, but the read and write of the data will change with the snapshot number. In the case of no write operation on the data shard, the data shard can still depend on the lower-level data shard. Lower-level data shards, and so on.

C. After the snapshot is created, the write operation of the data shard will trigger the data to be written into the new snapshot, which completes the redirected write of the data shard. The data shard will be used as the unique data of the snapshot. Access to the snapshot no longer asks lower-level dependencies.

D. The access to the snapshot reads the snapshot data smaller than the snapshot number, and the snapshot version of the data uses the same storage space as the original version, and the snapshot does not occupy space alone