Guidelines for Protecting Data using HP StorageWorks Storage Mirroring with Volume Shadow Copy Service (VSS) (T2558-96332, March 2009)

Setting up crash-consistent synchronous snapshots
For this strategy to work, you will have to initiate snapshots on both the source and target using either
Storage Mirroring’s in-band control feature or the Windows Task Scheduler. By using Storage Mirroring
to insert and run tasks at various points during the replication of data, you can coordinate a point-in-time
snapshot with real-time replication.
In order to synchronize snapshots on the source and target machines so that they contain the same
data, the process to create VSS snapshots on both the source and target servers is initiated via the
same task command. Here is how the process would work:
1. Storage Mirroring and an application are both running on the source. Only Storage Mirroring
is running on the target.
2. The application data is changing on the source and Storage Mirroring is capturing those data
changes and transmitting them to the target.
3. A script is launched that initiates a Storage Mirroring task command.
4. The Storage Mirroring task command is processed immediately on the source, initiating snapshot
creation on the source server. Then, the command is transmitted inline with the source replication
data to the target.
5. The data is applied on the target as it is received. Since the task command was inserted inline,
the replication data from the source is applied to the target first. When the target gets to the
Storage Mirroring task command, the target data will be in the exact same state as the source
data when the task command was processed by the source.
6. The target processes the Storage Mirroring task command and initiates snapshot creation on the
target. Since the Storage Mirroring task command is user-defined, you can insert any valid ex-
ecutable or batch file.
The following batch files outline an example of inserting a task command to initiate synchronized VSS
snapshots on the source and target servers. You should modify the batch files to accommodate your
own configuration.
Sample Implementation20