Solution : https://service.sap.com/sap/support/notes/423838 (SAP Service marketplace login required)
Key words : 
individual upgrade phases phase dbprep_chk            detailed information, set parameter   dbs/db2/pcon = 1, /sap/<sapsid>/sys/exe/run, db2 catalog tables sysibm, db2 pm            db2 pm, drop takes 6 times longer, planning guide sap web, sap system number stays, tuning newly-created tables, maintenance levelweb application server 610 6
Related Notes : 
       
| 705629 | DB2/390: Drop QCM#PUT tables before upgrade (re)start | 
| 647882 | DB2/390: PTF check in PREPARE overlooks missing PTFs | 
| 618675 | DB2/390: Bad performance in upgrade (RUN_INDC_UPG, ...) | 
| 529267 | DB2/390: Upgrade to 6.x - Troubleshooting | 
| 504959 | Upgrade Assistant on z/OS | 
| 434946 | DB2/390: R3szchk & R3ldclt for upgrade to >= 6.10 | 
| 423726 | DB2/390: DEFINE NO in the upgrade | 
| 422023 | Additional information on upgrading to BW 3.0A | 
| 401717 | Additional info on upgrading to SAP Web AS 6.10 (Basis) | 
| 400797 | DB2/390: Problems during an Upgrade on OS/390 USS | 
| 400565 | DB2/390: Upgrade: Optional checks | 
| 400466 | DB2/390: Upgrade BW 3.0A - free space | 
| 184399 | DB2/390: DDIC corrections (Releases 4.6A,4.6B,4.6C,4.6D) | 
| 183311 | DB2/390: Automated PTF Check | 
| 136806 | DB2/390: Upgrade: ICLI servers and database connect | 
| 81737 | DB2-z/OS: APAR List |