Solution : https://service.sap.com/sap/support/notes/206366 (SAP Service marketplace login required)
Key words : 
middleware -> message flow -> reorg -> processed bdocs, middleware -> message flow -> reorg -> middleware log, middleware -> settings -> maintain / define parametersentry, middleware -> settings -> general parametersentry, high io load occurs, additional key words crm, disc space increases, delivery class 'g', disk space requirement, long time -> recommendation
Related Notes : 
       
| 328791 | Quick deletion of trace files from the CRM server | 
| 318585 | |
| 214474 | |
| 206439 | Reorganization of tables in CRM Middleware |