979 - SE: Backing up and restoring Exchange 2013 DAGs

Important considerations

When backing up Exchange 2013 databases in a DAG environment by using the Server Edition Backup Client, note the following:

1. Unlike for Exchange 2010, the registry entry  HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ExchangeServer\V14\Replay\Parameters, with a DWORD entry of "EnableVSSWriter" with a value of 0 (zero), should not be applied and should be removed for Exchange 2013 if set.
2. If the Exchange server is a DAG member, and you select the "Exchange Group" or "Microsoft Exchange Writer" top level nodes for backup, Backup Pro will backup both the active and passive databases on that DAG member. (This has pros and cons - see "Default inclusions" below.)
3. If the database is the Active copy, the logs will be truncated as on a normal Exchange database when the backup completes (assuming that synchronisation is up to date with the Passive copy or copies).
4. If the database is a Passive copy, log truncation will not take place when the backup completes, but is slaved to the truncation event on the master Active copy.
5. It is possible to selectively backup the Active copies only, but this has to be done manually by selecting only the active databases in the VSS selection tree.

Default inclusions

As mentioned above, there are pros and cons to the default inclusion of both Active and Passive copies.

Pros:

• All databases are protected at all times on all members.
• If there is a failover/promotion to an active database, the whole database would not be sent in full but would patch as normal and continue. (This is a drawback on an Exchange 2010 DAG.)

Cons:

• Protecting all databases on all DAG members results in increased usage on the Storage Platform.
• Should you be selective in what you protect on DAG members - e.g. Active databases only - these could drop out of sync and be unprotected should you failover.

Note: Although confusing, it is possible to tell the difference between an Active and a Passive database in the Backup Pro logs: the word "Replica" is shown after the "Microsoft Information Store" on the Passive copy:

Active Copy:

Message: 14:54:30 Removed from backup: zzz:\Microsoft Exchange Writer\Microsoft Exchange Server\Microsoft Information Store\NEWEX1\4b465867-7b69-45dd-be47-577bfc44ba79\Logs\C:\Program Files\Microsoft\Exchange Server\V15\Mailbox\Mailbox Database 1913757852\E000000003B.log

Passive Copy:

Message: 14:54:33 Creating footprints for: PLUGIN:\29\zzz:\Microsoft Exchange Writer\Microsoft Exchange Server\Microsoft Information Store\Replica\NEWEX1\47d15a10-745b-45db-adf1-2fff5e353da2\Logs\C:\Program Files\Microsoft\Exchange Server\V15\Mailbox\Mailbox Database 2119963540\E000000006B.log

Backup options

1. Backup all databases, both Active and Passive, on both DAG members. This will use the most disk space, probably double, as all data will be protected twice.
2. Backup the Active databases on both DAG members, and manually change the backup selection should the role change. This will be more efficient in terms of disk space, but will carry a small admin overhead of changing the selection should the role change for the database.