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

snapshots, this strategy produces snapshots of the exact same data on both the source and target.
To use synchronous snapshots, you need to use Storage Mirroring’s in-band control feature to kick
off snapshots (as opposed to using the VSS built-in scheduling feature). Synchronous snapshot
strategies work well for transactional applications, such as databases.
There are two options for creating synchronous snapshots:
• Crash-Consistent Synchronous Snapshots: A crash-consistent state means that at any given
moment, the target represents a single point in time from the source, as it might be if the source
machine was powered off or crashed abruptly during operation. Unlike data-consistent snap-
shots, crash-consistent snapshots do not require the database application on the source machine
to be stopped at any point, thus minimizing downtime.
• Data-Consistent Synchronous Snapshots: A data-consistent state means that the target represents
a known quiesced file state on the source, such as when an application is temporarily shut
down. It typically takes less time to recover applications from a data-consistent state. This
strategy is identical to the Crash-Consistent Synchronous Snapshots strategy, except that the
database application is stopped momentarily in order to get the data in a consistent state.
Setting up asynchronous snapshots
When using the asynchronous snapshot strategy, no changes need to be made to the snapshot
schedule on the source. On the target, snapshots either have to be made manually or be initiated by
a script from Windows Task Scheduler. Either way, the target will have to be paused by Storage
Mirroring to stop replication from occurring while the snapshot is being taken, then resumed after the
snapshot is taken.
NOTE:
The command to perform the snapshot itself using VSS is:
vssadmin create shadow /for=X:
where X: is the drive where the snapshot is made.
The following instructions contain step-by-step procedures for incorporating the DTCL commands used
in the Text Client into a DTCL script which will allow you to automate the pause and resume process
from a batch file.
NOTE:
Pausing and resuming the target can be manually initiated through the Management Console or Text
Client, or you can use DTCL commands to script it. For more information about using the Management
Console or Text Client, see the HP StorageWorks Storage Mirroring User’s Guide .
1. Prior to the snapshot process starting, you will want to pause execution of operations on the target.
To do this, create a batch file called presnapshot.txt using the following sample file. Save
this file to the location where Storage Mirroring is installed.
NOTE:
These sample batch files are available at http://www.hp.com/support.
After you modify the sample scripts, save them with a new name to remove the SAMPLE_ prefix.
Copy the scripts to the directory where Storage Mirroring is installed.
Guidelines for Protecting Data using HP StorageWorks Storage Mirroring with Volume Shadow Copy
Service (VSS) 17