Backup issues and limitations with Exchange 2010 and DAG
I have come up with the following conclusions after testing some backup functionalities with Windows Server Backup and Exchange 2010 with DAG.
There are some limitations that we'll have to be aware of:
1. Windows Server Backup (WSB)
When using Windows Server Backup to backup an Exchange 2010 database the backup fails under the following conditions:
- Each database and associated logs are stored on a dedicated LUN (these are presented by the SAN software to the OS as separate volumes as expected in Disk Management)
- The database LUN is presented via a mount point
- Some database copies on the server are not active
For example, two mailbox servers that are DAG members (SERVER1 & SERVER2), and two mailbox databases (MBX1 & MBX2).
If both mailboxes databases are active on one server, and a backup of MBX1 is made using Windows Server Backup, the backup will be successful. However if the mailbox database that is not being backed up is inactive (i.e. active on the other server) the backup fails with a consistency check error.
Source: Microsoft-Windows-Backup
Date: 15/12/2009 15:51:16
Event ID: 565
Task Category: None
Level: Error
Keywords:
User: SYSTEM
Computer: LONEX5002.QAEUROPE.NOM
Description:
The consistency check for the component '0139dd0d-a73d-4fec-a0c5-04377b915413'\'Microsoft Exchange Server\Microsoft Information Store\LONEX5002' has failed. The application 'Exchange' will not be available in the backup created at '?2009?-?12?-?15T15:51:04.281250000Z'. Review the event details for information about consistency check issues.
This issue is still being investigated at this moment.
2. DPM 2010 (beta) or every other 3rd party.
The difference here from WSB is that DPM is aware of the passive copies and will perform a successful backup of both the active and the passive copies.
The limitation comes when performing a restore: (limitation of the Exchange Replica VSS Writer).
You cannot perform a restore of the passive database copies in the original location because of the Replica VSS Writer that can only backup, but NOT perform a Restore. The only option would be to perform the Restore to an alternate location and manually roll the databases forward to bring them in a clean shutdown.
For more info, please check:
Exchange VSS Writers
https://msdn.microsoft.com/en-us/library/bb204080.aspx
"The Store Writer is available on any mailbox server and is responsible for backup/restore of active databases. The Replication Writer is available on the passive node of DAG server. The Replication Writer supports backup functionality for a selected database where the shadow copy is taken against the replicated instance of the database and transaction log files. Backups taken by the Replication Writer can be restored to the active database location by using the Store Writer.
During a restore, the backup/restore application instructs the Exchange Store Writer to coordinate with the Exchange store (operating on behalf of the requestor) to verify the restore targets, rename the database file if necessary, and then replay the transaction logs as needed. The Store Writer supports both backups and restores, while the Replication Writer supports only backups
Understanding Backup, Restore and Disaster Recovery
https://technet.microsoft.com/en-us/library/dd876874.aspx
Be aware of these limitations when using VSS for backup and restore of Exchange data:
- The VSS plug-in that ships with Exchange 2010 can be used to back up volumes containing active mailbox database copies or standalone (non-replicated) mailbox databases only. It can't be used to back up volumes containing passive mailbox database copies. To back up passive mailbox database copies, you need either Microsoft System Center Data Protection Manager or a third-party Exchange-aware VSS-based application.
- Passive mailbox database copies are backed up using a separate VSS writer in the Microsoft Exchange Replication service. The Microsoft Exchange Replication service VSS Writer doesn't support restores. Although you can back up a passive mailbox database copy using Microsoft System Center Data Protection Manager or a third-party Exchange-aware VSS-based application, you can't perform a VSS restore directly to a passive mailbox database copy. However, you can perform a VSS restore to an alternate location, suspend replication to the passive copy, and then copy the database and log files from the alternate location to the location of the passive database copy in the file system.
13.05.2010:
Update:
After further investigation it has been concluded that the above mentioned issue is actually a limitation of Windows Server Backup and in conclusion the TechNet articles have been modified accordingly:
Using Windows Server Backup to Back Up and Restore Exchange Data
https://technet.microsoft.com/en-us/library/dd876851.aspx
“If a server hosting the data being backed up is a member of a database availability group (DAG) and hosts both active and passive database copies, you must disable the Microsoft Exchange Replication service VSS writer. If the Microsoft Exchange Replication service VSS writer is enabled, the backup operation will fail.”