I think that there is a wrong assertion in documentation about Storage Requirements for varchar datatypes.

https://mariadb.com/kb/en/mariadb/data-type-storage-requirements/

Documentation says (in "String data types" section):

Data Type: VARCHAR(M), VARBINARY(M)
Storage Requirement: M + 1 bytes if column is 0 – 255 bytes, M + 2 bytes if column may require more than 255 bytes

As I am concern, this should be:

Data Type: VARCHAR(M), VARBINARY(M)
Storage Requirement: len + 1 bytes if column is 0 – 255 bytes, len + 2 bytes if column may require more than 255 bytes

So space depends on actual value length (len) and not actual definition (M)...