Solution : https://service.sap.com/sap/support/notes/744735 (SAP Service marketplace login required)
Key words : 
iseries-specific ascii/unicode inplace code<z1> page conversion, describe platform-dependent database object attributes, ascii/unicode code page conversion, standardascii/unicode code page conversion, ascii/unicode inplace conversion, code page conversion/system copy, homogeneous migration               homogeneous migration works, avoid additional downtime due, r3load export/import mechanism, normal export/import process
Related Notes : 
       
| 800791 | IBM i: In-place Code Page Conversion ASCII to Unicode | 
| 777024 | BW3.0 and BW3.1 System copy (supplementary note) | 
| 771209 | NetWeaver 04: System copy (supplementary note) |