current environment we can Active directory two DC and DR and same site (not configure site) is default first site
and Exchange 2013 have 6 Mailbox Server in DC and 3 Mailbox server (all server CAS + MBX roles). and one CAS server only for management and witness and it is VM can should can running in DC or DR (current running in DC)
we have been migrate almost user to office365 and only still about 1000 user on local .Now we want remove some mailbox server to how it can running in DC and DR , it mean is in case DC shutdown maintain electronic or failure then it can running in DR otherwise if DR failure then it is working normal in DC
we are planning remove three server in DC and one server in DR to remain DC=2 and DR=2
all exchange the same site and the same subnet .active directory only one site is "Default-First-Site-Name" .So the future if have DAG 2:2 then need one or two witness server ? if one witness on DC then if all server DC down then DR can up cluster and DAG normal ?
@Tien Ngo Thanh the numbers in the 2:2 ratio mean 2 servers in one site, 2 in another, so really you just want a 4 node dag all in same site (4:0 DAG). In this case, you would only need the one FSW, he just helps break ties between even votes.