588 Implementing the IBM Storwize V5000 Gen2 with IBM Spectrum Virtualize V8.1
10.9.3 Changing the system parameters
When you want to change system parameters specific to any remote copy or Global Mirror
only, use the chsystem command. The chsystem command features the following parameters
for MM/GM:
-relationshipbandwidthlimit cluster_relationship_bandwidth_limit
This parameter controls the maximum rate at which any one remote copy relationship can
synchronize. The default value for the relationship bandwidth limit is 25 MBps, but this
value can now be specified 1 - 100,000 MBps. The partnership overall limit is controlled by
the chpartnership -linkbandwidthmbits command, and must be set on each involved
system.
-gmlinktolerance link_tolerance
This parameter specifies the maximum period that the system tolerates delay before
stopping Global Mirror relationships. Specify values 60 - 86,400 seconds in increments of
10 seconds. The default value is 300. Do not change this value except under the direction
of IBM Support.
-gmmaxhostdelay max_host_delay
This parameter specifies the maximum time delay, in milliseconds, at which the Global
Mirror link tolerance timer starts counting down. This threshold value determines the
additional effect that Global Mirror operations can add to the response times of the Global
Mirror source volumes. You can use this parameter to increase the threshold from the
default value of 5 milliseconds.
-gminterdelaysimulation link_tolerance
This parameter specifies the number of milliseconds that I/O activity (intercluster copying
to an auxiliary volume) is delayed. This parameter enables you to test performance
implications before Global Mirror is deployed and a long-distance link is obtained. Specify
a value of 0 - 100 milliseconds in 1-millisecond increments. The default value is 0. Use this
argument to test each intercluster Global Mirror relationship separately.
-gmintradelaysimulation link_tolerance
This parameter specifies the number of milliseconds that I/O activity (intracluster copying
to an auxiliary volume) is delayed. By using this parameter, you can test performance
implications before Global Mirror is deployed and a long-distance link is obtained. Specify
a value of 0 - 100 milliseconds in 1-millisecond increments. The default value is 0. Use this
argument to test each intracluster Global Mirror relationship separately.
-maxreplicationdelay max_replication_delay
This parameter sets a maximum replication delay in seconds. The value must be a
number 1 - 360. This feature sets the maximum number of seconds to be tolerated to
complete a single I/O. If I/O can’t complete within the max_replication_delay the 1920
event is reported. This is the system-wide setting. When set to 0, the feature is disabled.
This applies to Metro Mirror and Global Mirror relationships.
Important: Do not set this value higher than the default without first establishing that
the higher bandwidth can be sustained without affecting the host’s performance. The
limit must never be higher than the maximum that is supported by the infrastructure
connecting the remote sites, regardless of the compression rates that you might
achieve.
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