Exchange Site resilency

DigitBoy
DigitBoy used Ask the Experts™
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Dear experts,


in exchange 2010 you have DAG HA (=automatic failover) and Site resilency (=manual failover & equal to disaster recovery mode). If there are 2 datacenters with 1 AD site (stretched) HA automatic failover is supported. If there are 2 AD sites across 2 datacenters, the recommended solution should be "site resilence" mode. => Is this correct? Because following MS engineer this is supported, but I'm doubting. (I read a lot articles and forums, but is not very clear)

If in DAG there are 3 members, 2 in DC1 site & 1 in DC2, [formular =>(N/2)+1= ?)], do I need a FSW? (Normally not). And also in "majoirty node" in this scenario can I still create a FSW in DC1 and an alternate FSW in DC2 and enable DAC for 1 AD site with HA without "site resilence" in case the 2 servers in DC1 goes down or network connection between the 2 Datacenters are broken?

Or ideal solution would be in DC1 2 mbx servers and in DC2 1 mbx server in same DAG; the 2 servers in DC1 in HA and server in DC2 using as DR (=site resilence); 1 FSW in DC1 and in DC2 an "Alternate FSW" and also DAC enabled.  Is this correct?

More clear information needed please?

K rgs
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BusbarSolutions Architect

Commented:
you will need the FSW anyway because in failure you will move from odd to even no. of nodes, and they are all supported it depends on what are you looking for, the stretched AD site gives you automatic failover but it might has its drawbacks.

Author

Commented:
Hi busbar,

so it means that in stretched AD site across 2 datacenters the HA is supported and there is no need for "site resilence/Disaster Rec site".
And your recommendation is to create FSW anyway in DC1. Am I right? And what about:

"Or ideal solution would be in DC1 2 mbx servers and in DC2 1 mbx server in same DAG; the 2 servers in DC1 in HA and server in DC2 using as DR (=site resilence); 1 FSW in DC1 and in DC2 an "Alternate FSW" and also DAC enabled.  Is this correct?"

K Rgs
Senior Systems Admin
Top Expert 2010
Commented:
AD Site Across 2 datacenters does require some level of disaster recovery if one physical datacenter fails for some reason. Since you have two DAG nodes in one DC and one in the other, if the first DC goes down the DAG will lose quorum and you'll have to initiate a Disaster Recovery plan (This involves using DAC to force eviction of the two servers in site 1 and initiating a FSW in site 2 to restart the cluster). Failover isn't automatic in this situation. It should be automatic if only one of the servers fails, but I haven't actually tested that out before. DAC Assists in the full site failover by including cmdlets in Powershell that allow you to evict nodes and assign a fileshare witness for the second datacenter. Since you have three MBX servers, you don't need to have a FSW for normal operation, but if site one fails and you have to initiate a site failover, you will need to switch the quorum model from Node Majority to FSW (As mentioned, DAC helps with this).
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BusbarSolutions Architect

Commented:
I agree with acbrown2010, site recovery is a site recovery, the definite solution for the FSW is to place it in a 3rd site.

also the recommendation is valid, but I will go with 2 nodes in HQ to prevent mailbox database activation on the DR site just because a disk failure, I will fight to keep it as much as I can at HQ

Author

Commented:
Thanks a lot guys for feed back,but still one of my questions were if in stretched AD a DAG HA (automatic failover) is supported or not (some MVPS says it is)? Is this true or not?

And for second question you already answered.

Can you give me more info regarding the first question please?

K rgs

Author

Commented:
To place FSW in 3 rd site is a big misconception. See Microsoft Exchange 2010 misconceptions and not really logical.
BusbarSolutions Architect

Commented:
the miss-conception talks about WAN connectivity only, not a full site failure. however it is still valid configuration

Author

Commented:
Hi busbar,

when you said "however it is still valid configuration". Did you mean for "stretched AD a DAG HA (automatic failover)"?

K rgs

Author

Commented:
Can someone answer question nr 1 please?

Author

Commented:
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