You were right, somehow I really did miss to change vid/pid. Now installation goes smooth but after restart synology complains that my disks were moved from another DS3615xs and wants to reinstall/update os. Seem it can not mount /dev/md0 in the boot process, so falls back to installer, but in the installation process, disks are recognized correctly. So it looks a timing issue to me, will look into it. I was wondering how to change vid/pid. I'm facing same issue.