Exchange DAG Configuration

[ITGURU]

I've currently got 2 sites running exchange server both interlinked IP-IP and accessible from the internet.

 

 

at both sites i've got 1 DAG which includes both exchange servers for each separate site with a File share witness on that site so if one server goes now it will failover to the other.

 

I now want to add to the mix so that a copy of site's 1 databases are mirrored to site 2 so in event of internet failure to the main site, users can get to the mailboxes from site 2.

 

Could someone do a quick diagram of what i need in the way of DAG and placement of the witness.

thanks in advance.

[Domino]

Well, there's a lot to consider here.

 

Which exchange version?

How is the namespacing setup between the servers?

When you say "a fileshare witness on that site" is that a single or two FSW? Either way achieving quorum with that could be a manual process.

 

Ideally, a two member DAG would have a FSW at a tertiary site. That way a single site failure could be survivable (as 2 votes are available for DB activation out of 3 total).

[ITGURU]

Well, there's a lot to consider here.

 

Which exchange version?

How is the namespacing setup between the servers?

When you say "a fileshare witness on that site" is that a single or two FSW? Either way achieving quorum with that could be a manual process.

 

Ideally, a two member DAG would have a FSW at a tertiary site. That way a single site failure could be survivable (as 2 votes are available for DB activation out of 3 total).

- Exchange 2016

2 AD Sites, DC's at both sites for the domain

Exchange server on each site are all part of the same domain.

 

Single FSW on each site for the 2 servers hosting that sites exchange DB.

[ITGURU]

Well, there's a lot to consider here.

 

Which exchange version?

How is the namespacing setup between the servers?

When you say "a fileshare witness on that site" is that a single or two FSW? Either way achieving quorum with that could be a manual process.

 

Ideally, a two member DAG would have a FSW at a tertiary site. That way a single site failure could be survivable (as 2 votes are available for DB activation out of 3 total).

here's current setup

[Domino]

So, what you have here would survive a server failure, but not a site failure.

 

Normally, including FSW, you'd weant an odd number of votes in a DAG group. So when a member is missing more than half the total votes remain, meaning a cluster election can be won. More here: https://practical365.com/exchange-server/exchange-2016-database-availability-groups/

 

However it occurs to me I thought you could only have 1 FSW per DAG (not counting the alternate FSW setting, which doesn't work like you'd think). So do you actually have 2 DAGs here, with one exchange server in each?

[ITGURU]

So, what you have here would survive a server failure, but not a site failure.

 

Normally, including FSW, you'd weant an odd number of votes in a DAG group. So when a member is missing more than half the total votes remain, meaning a cluster election can be won. More here: https://practical365.com/exchange-server/exchange-2016-database-availability-groups/

 

However it occurs to me I thought you could only have 1 FSW per DAG (not counting the alternate FSW setting, which doesn't work like you'd think). So do you actually have 2 DAGs here, with one exchange server in each?

 

Yes correct what I have setup is a server failure per site,(2 servers per site each hosting a duplicate of the other server databases) however i'm looking to add Site failure, so cant work out what i need in terms of DAGs and witness locations, which is the bit i'm looking for a bit of assistance with. Thanks,.

[Domino]

You'd either want an extra server in each site, and extend the opposing sites DAG to it, or to go down to one DAG and have all the mailbox DBs in a single one across all servers.

 

Neither of these will give you full automatic failover without having the FSW in a third site. Attached is my setup, each region is setup like that.

 

[ITGURU]

You'd either want an extra server in each site, and extend the opposing sites DAG to it, or to go down to one DAG and have all the mailbox DBs in a single one across all servers.

 

Neither of these will give you full automatic failover without having the FSW in a third site. Attached is my setup, each region is setup like that.

 

[ATTACH=CONFIG]56519[/ATTACH]

If i put all 4 servers into a SINGLE DAG so that all 4 hold copies i presume i then set one of the servers in SITE A for site's A mailboxes as active and one of the servers in SITE B for site B's local mailboxes as ACTIVE and the other 2 remain passive?

 

Where would witness be located for the single DAG?

[Domino]

Ideally the FSW would be in a third site. That way it's available in a site failure situation to provide Quorum for either Site.

 

If that's not possible, you'd be looking at one site that was able to activate if the other went down, and one which would require manual activation if the site with the FSW went down.

[ITGURU]

Ideally the FSW would be in a third site. That way it's available in a site failure situation to provide Quorum for either Site.

 

If that's not possible, you'd be looking at one site that was able to activate if the other went down, and one which would require manual activation if the site with the FSW went down.

 

Can i have a configuration where on each site, there is automatic failover to the second server, but in even of SITE link failure, i can do manual activation and activate the databases at the second site so users can still access externally?

[Domino]

I'm only talking site failures in the above. When Three of your Four Exchange servers are up you should have no issues with failover.