Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
This message is a piece of history, and you will not see it in practice anymore. Let me tell you the story. A holder can rest on disk in two ways: in a database, or in a filesystem. At first, only the database way was built. If you asked for the filesystem way, the engine refused by name, rather than quietly storing your data in the database and letting you believe it was in a filesystem. That would have been a lie about where your data lives. Then the filesystem way was built. Now a holder declared with where filesystem becomes a directory at the path you give, and each member is a single file. You can name the filesystem, or leave it out and land below the declared mount. And each statement lands whole or not at all, using a staged directory and one atomic rename. So this refusal is no longer raised. It stays in the catalogue as a record, so old logs still make sense. If an old log shows it, read it as history. Nothing to fix today.
Text from the Rush engine's error catalogue.