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

For any replication set that may generate a significant amount of data, you should enable compression
for the connection. For more information about enabling compression, see the HP StorageWorks
Storage Mirroring User’s Guide. Storage Mirroring compression algorithms were designed to minimally
impact processor utilization for replication in most environments while providing significant bandwidth
savings. If you notice an impact on performance while compression is enabled in your environment,
either adjust to a lower level of compression, or leave compression disabled.
Configuring memory usage
Storage Mirroring uses memory to queue operations and data on both the source and target. Since
the source server is typically running a production application, it is important that the amount of
memory Storage Mirroring and the other applications use does not exceed the amount of RAM in the
system. If the applications require more memory than there is RAM, the system will begin to swap
pages of memory to disk and the system performance will degrade.
For instance, SQL Server will use all of the available system memory when needed by default, and it
may use almost all of the system memory during high-load operations. These high-load operations
are precisely what cause Storage Mirroring to need memory to queue the data being changed by
SQL Server. On a server with 1 GB of RAM running SQL Server and Storage Mirroring, you might
configure SQL Server to use only 512 MB and Storage Mirroring to use 256 MB, leaving 256 MB
for the operating system and other applications on the system. Many other server applications will
use almost all system memory by default, so it is important to check and configure applications
appropriately, particularly on high-capacity servers.
Guidelines for Protecting Data using HP StorageWorks Storage Mirroring with Volume Shadow Copy
Service (VSS) 13