Administrator Guide

/connectivity/local-com/
The local role context contains the configuration information related to inter-director communication within the current
cluster.
The local role does not have any associated properties.
Managing and Monitoring back-end network
For high availability each director should have multiple paths to each storage volume. Environmental issues such as network
congestion or array problems can affect the availability and performance of these paths. For more details, see the Best
Practices documents for metro node. Metro node monitors the latency of each back-end IT Nexus, and there is a possibility
of encountering poorly performing back-end paths. Metro node has several mechanisms to limit the performance impact:
Taking a Back-End IT Nexus with High Latency Out of Service
If an I/O takes greater than 1 second to complete on an ITL (Initiator-Target-LUN on an IT Nexus), then the ITL and IT accrue a
penalty where the allowed command limit for the ITL is reduced from five to one. If the accumulated penalty for an ITL exceeds
2 seconds, then the command limit on the ITL is reduced to zero indicating that no more commands are allowed on this ITL. Due
to high latency, if greater than 20 ITLs on an IT Nexus are penalized, then the IT Nexus is marked degraded and metro node
automatically stops using the IT Nexus for host-based I/O until performance improves.
NOTE:
If the last available path to a Logical Unit is marked degraded, then it cannot be taken out of service, and a penalty
is applied to allow a single I/O at a time to the LU. One ITL per Logical Unit per director continues to receive commands.
Once the performance improves the metro node automatically restores the default outstanding I/O count to the Logical
Unit.
Degraded back-end IT Nexuses can be monitored using the VPlexcli command back-end degraded list. For more details,
see CLI Reference Guide for metro node. Due to continuous high latency, when an IT Nexus is marked degraded, then this
command lists the Degradation Reason as Degraded performance.
If a user finds that a degraded IT Nexus has been restored to health, it is also possible to manually restore its use through the
VPlexcli command back-end degraded recover.
Marking a Back-End IT Nexus Isolated due to Unstable
Performance
If a back-end IT path is found to cycle between degraded and undegraded three times within a 30 minute period, then the IT
Nexus is considered unstable and the metro node automatically stops using the IT Nexus for host-based I/O. In this state, the
VPlexcli command back-end degraded list list the Degradation Reason as Isolated due to unstable performance.
In this case, the IT Nexus remains degraded until the user manually restores it using the VPlexcli command back-end
degraded recover. It is also possible that threshold reaches to its four-hour default value, after which the IT nexus is
marked as performance degraded while the recovery process checks its health before undegrading it (and automatically
re-enabling the path to serve host-based I/O again if the performance tests pass). If the intermittent latency issue is continued
on the IT Nexus and the user is unable to address the root cause, then it is advised to engage metro node Customer Service to
manually mark the IT Nexus degraded to remove the path from use until the underlying issue is resolved.
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Configure the WAN Network