The machine was using over 90% diskspace and the cratedb note went into read-only mode.
I deleted lots of files and the server has now over 30% of available space.
The cratedb node was restarted, everything is green in the admin console but it is still in read-only mode.
It would be great if the node could detect that disk space is below the threshold again and automatically make the node writable, instead of having to manually update each table.