I tried to add an additional disk and made some progress. Synology Assistance successfully take the PAT file, go through successfully the following steps
1. network setting
2. format system area
3. format data area - NA
4. install DSM
When it come to step 5, it fails.
5. write config file
When checking on the VM, the following is shown, and the VM doesn't boot up
GRUB loading, please wait...
Error 22