Can anybody explain? What other stuff takes the disk space?
If an external block device is not available, the message-spool, configuration database, logs, diagnostics information, OS etc all share the same disk space. We reserve the bulk of the disk for the OS and configuration database, leaving limited space for the message-spool, logs and diagnostics. It is possible to have disk free and no spool space left, despite having very few messages-spooled. To resolve it, you can delete old log files, backup files to free up some spaces. Ultimately, it is recommended to use a separate disk for message-spool data.
@emyrpetersen you can have look on https://solace.community/discussion/111/delete-old-messages-on-solace