Full disk on a MySQL cluster: binary logs, Group Replication, and a migration that leaves no room for mistakes

Tue, 14 Oct 2025 08:03:00 +0100

The alert came on a Monday morning, wedged between three meetings and a coffee that was still hot. “Filesystem /mysql at 85% on the primary node.” On another node it was 66%, on the third 25%. In a cluster, when the numbers don’t match across nodes, there’s always something going on underneath.

The first question that comes to mind is “how much space do we need?” But that’s the wrong question. The right one is: “why is it filling up?”

Innodb-Cluster on Ivan Luminaria

Full disk on a MySQL cluster: binary logs, Group Replication, and a migration that leaves no room for mistakes