i have a forest and first DC having 3 roles another additional DC having 2 roles so what is advantages and how to transfer roles? in case if i want to reboot the both DC's (after patching) it is necessary to transfer roles to new additional DC?

No, it isn't necessary.

 

 

Then if advantage of installing "i have a forest and first DC having 3 roles another additional DC having 2 roles"

Hello,

You won't get proper assistance asking questions like that. You need to do your own research and then ask specific questions if there is something you don't understand.

Have you read : https://support.microsoft.com/en-us/kb/197132 ?

Hi,

Just reboot DC after update installation, there is no need to transfer roles. 

After all roles transfer is not a simple process, unless you want to deactivate the current device and enable a new one. And, since there are 2 DCs on your environment, they may be configured for fault tolerance. The other DC can responsible for related work during one DC rebooting.

DC may also other roles installed except for AD DS, such as DNS, DHCP or any other. I am wondering what are the 3 roles on first DC, and what are the 2 roles on secondary DC? 

Best Regards,
Eve Wang      

Frist DC forest level FSMO roles and adiitional DC Domain level FSMO roles

Hi,

Forest level: Schema Master and Domain Naming Master.
Domain level: PDC Emulator, RID Master and Infrastructure Master.

There is only one Schema and domain Naming Master in the forest, and by default the first DC of root forest would hold these masters. And each domain has its own PDC Emulator, RID and Infrastructure Master, by default the first DC of this domain would hold theses 2 domain level roles. Its difficult to identify the advantage/disadvantage. Just configured by default.

Links below provide information about transfer FMSO, just for your reference.
Transferring an Operations Master Role
https://technet.microsoft.com/en-us/library/cc816946(v=ws.10).aspx
Transferring FSMO Roles in Windows Server 2008
http://social.technet.microsoft.com/wiki/contents/articles/832.transferring-fsmo-roles-in-windows-server-2008.aspx

Also, as mentioned above, there is no need to do this if DC temporarily shutdown. 

Best Regards,
Eve Wang