Multistreaming Backups for Exchange Databases
Applies to: Exchange 2010 or later
By default, each database in the subclient is backed up one at a time. You can back up each database concurrently (in parallel) using multistreamed backups. To back up Exchange databases using multistreaming, you configure the maximum number of streams.
Planning a Multistreamed Backup
When you use multistreaming to back up your Exchange databases, the maximum stream value that you set depends on your environment.
In a stand-alone environment, the minimum possible maximum streams value is 1 and the maximum possible value is the number of databases.
In a DAG environment, determining the maximum streams value is more complex. Nodes are assigned in rounds based on which node has the most databases of all the nodes involved in the backup. However, if a node was assigned a stream in the previous round, it does not qualify for a stream again until all other nodes are assigned a stream in subsequent rounds.
Example: DAG Environment
In this example, you have three nodes with a total of 20 databases to be backed up. The following is the database distribution:
Node 1: 6 databases
Node 2: 5 databases
Node 3: 9 databases
If you set the maximum number of streams to 7, then nodes are assigned the following number of streams each round:
|Round||Node 1||Node 2||Node 3||Description|
|1||1||1||1||Each node is assigned a stream.|
|2||1||Node 3 is assigned a stream because it has the most (8) databases. It will not qualify for a stream in round 3 and round 4.|
|3||1||Node 1 is assigned a stream because it has the most (5) databases. It will not qualify for a stream in round 4.|
|4||1||Node 2 is assigned a stream because it is the only node that qualifies for a stream. Now that all the nodes have been assigned streams, all nodes qualify for any remaining streams.|
|5||1||Node 3 is assigned the last remaining stream because it has the most (7) databases.|
After the streams are assigned to each node, the databases are backed up in descending order according to size (that is, starting with the largest database).
- If the backup on a volume is completed (that is, the streams assigned to that volume become idle), the idle streams are made available to the other volumes on the node. However, idle streams do not become available across nodes; they become available only across volumes.
- If the backup in a DAG environment is to tape storage and there are more nodes than tape storage devices, then the number of nodes that are backed up at one time is limited to the number of tape storage devices that are available even though the maximum stream value is greater. All other nodes wait until a tape storage device is available for backup.
- The recommended minimum value in a DAG environment is equal to the number of nodes that are involved in the backup.
- The maximum value possible is the total number of databases to be backed up. However, the higher the maximum stream value, the greater the processing load on the Exchange server.
- There must be enough space on the Exchange server to accommodate all VSS snapshots.