To plan for using the Global Mirror feature
in noncycling mode, consider these requirements.
All components in the
SAN must be capable of sustaining the workload that is generated by
application hosts and the Global Mirror background
copy process. If all of the components in the SAN cannot sustain the
workload, the Global Mirror relationships
are automatically stopped to protect your application hosts from increased
response times.
Note: Errors about Global Mirror operations
are not logged.
When you use the noncycling Global Mirror feature,
follow these best practices:- Use Spectrum Control or
an equivalent SAN performance analysis tool to monitor your SAN environment.
The Spectrum Control provides
an easy way to analyze the Lenovo Storage V7000 performance
statistics.
- Analyze the Lenovo Storage V7000 performance
statistics to determine the peak application write workload that the
link must support. Gather statistics over a typical application I/O
workload cycle.
- Set the background copy rate to a value that can be supported
by the intersystem link and the back-end storage systems at
the remote clustered system.
- Do not use cache-disabled volumes in noncycling Global Mirror relationships.
- Set the gmlinktolerance parameter to an appropriate
value. The default value is 300 seconds (5 minutes).
- When you complete SAN maintenance tasks, take one of the following
actions:
- Reduce the application I/O workload for the duration of the maintenance
task.
- Disable the gmlinktolerance feature or increase the value of the gmlinktolerance parameter.
Note: If
you increase the value of the gmlinktolerance parameter
during the maintenance task, do not set it to the normal value until
the maintenance task is complete. If the gmlinktolerance feature is
disabled for the duration of the maintenance task, enable it after
the maintenance task is complete.
- Stop the Global Mirror relationships.
- Evenly distribute the preferred nodes for the
noncycling Global Mirrorvolumes between the nodes in the systems. Each volume in an I/O group has a preferred
node property that can be used to balance the I/O load between nodes
in the I/O group. The preferred node property is also used by the Global Mirror feature
to route I/O operations between systems. A node that receives
a write operation for a volume is
normally the preferred node for that volume.
If the volume is in a Global Mirror relationship,
the node is responsible for sending the write operation to the preferred
node of the secondary volume.By
default, the preferred node of a new volume is
the node that owns the fewest volumes of
the two nodes in the I/O group. Each node in the remote system
has a set pool of Global Mirror system
resources for each node in the local system. To maximize Global Mirror performance,
set the preferred nodes for the volumes of
the remote system to use every combination of primary nodes and secondary
nodes.
- Don't run rmvdisk -force for
a secondary volume in a running relationship.
- Stop all relationships before upgrading a cluster
containing secondary volumes.
- If the secondary volume is the source of a Fiber
Channel map, stop the relationship before starting the Fiber Channel
map.