Can we have CU8 on one server and keep other on CU1 Exchange 2016 In DAG

We have a DAG with 3 Exchange 2016 servers. One server have been affected by ransomware and we have shutdown it.   Now we are going to rebuild the brand new server to include it.

Questions: The Exchange 2016 CU1 is installed on the servers and we are not able to find it its installer to install it on new server.  Can we install Exchange 2016 CU8 on one server in DAG and keep other servers on Exchange 2016 CU1?

Or we have to upgrade other servers as well to CU8 after installing CU8 on new server?

Please guide us how we need to proceed.
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Muhammad AsifSenior Solutions ArchitectAsked:
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IvanSystem EngineerCommented:
Hi,

all Exchange DAG servers should run the same CU version, so if you cannot find CU1 (which is very old btw), you should upgrade those 2 servers to CU8, and then deploy new server.

Regards,
Ivan.
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Muhammad AsifSenior Solutions ArchitectAuthor Commented:
Hi Ivan,

Can you provide any link or article which have all this information. I would really apperciate if you can provide me any helpful link or article in this regard.
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Hasin Ahmed ChoudharyExchange AdministratorCommented:
Hello Muhammad,

If you upgrade the other two servers to CU8, and try to restore the failed server using recover server option to the same CU8, I am sure that it will fail.

Solution 1)

You will have to recover to the same CU. If you can't find CU file, you need to raise MS support to provide old CU1 setup file.

Solution2)

To maintain DAG feature, you can upgrade the rest of two servers to CU8 and introduce new server (with Cu8) with a new name to DAG.
You can remove failed server details from DAG.
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Todd NelsonSystems EngineerCommented:
Can we install Exchange 2016 CU8 on one server in DAG and keep other servers on Exchange 2016 CU1?

You can but it would not be ideal mixing CU1 (released May 2016) and CU8 (released Dec 2017) in a long term scenario.  However, you should not upgrade all of the servers at once either.


Or we have to upgrade other servers as well to CU8 after installing CU8 on new server?

Ideally, and because of the Exchange teams support stance, you will want to update the servers with Exchange 2016 CU1 to CU8 (or CU7) soon.  Microsoft only supports the two recently released CUs.  At this point in time, only CU7 and CU8 are supported for Exchange 2016.  CU9 is anticipated in March 2018, and at that time only CU8 and CU9 will be supported.
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