MaxScale should be able to react when some node of a cluster hits a disk-full situation.
For instance, if the master in a master-slave cluster hits a disk-full situation, MaxScale should promote some existing slave to master and remove the old master from the cluster. That way, a client connected to MaxScale would not necessarily detect anything special at all.
In order to do that, MaxScale must be able to detect that a disk-full situation has occurred. It's difficult and unreliable to do that using MariaDB itself, for instance, by trying to create a table and assuming it was a disk-full situation in case the creation fails or the attempt ends with a timeout. Further, that approach would not allow MaxScale to become aware of the situation before the disk actually becomes full.
A more reliable way would be to actually monitor the disk-space situation on the node and use that for the decision making, but arranging that is rather complex and fragile.
A robust solution would be if there were a pseudo table or pseudo tables in information_schema using which information about the node could be found out. For instance as follows:
With this information available, MaxScale could automatically take corrective action in case the amount of used disk-space grows above, say, 90%.