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The MDM cluster
The MDM functions as the monitoring and configuration agent of VxFlex OS and is
used mainly for management. A multi-MDM environment consists of one Master
MDM, while the others function as Slaves or Tie-Breakers.
The MDM serves as the monitoring and configuration agent of VxFlex OS. The MDM is
mainly used for management which consists of migration, rebuilds, and all system-
related functions. No I/O run through the MDM.
To support high availability, three or more instances of MDM run on different servers.
In a multi-MDM environment, one MDM is given the Master role, and the others act as
Slave or Tie Breaker MDMs.
The MDM cluster comprises a combination of Master MDM, Slave MDMs, and Tie
Breaker MDMs.
The following terms are relevant to the MDM, the building blocks of the MDM cluster:
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MDM
Any server with the MDM package installed. An MDM can be given a Manager or a
Tie Breaker (default) role, during installation. MDMs have a unique MDM ID, and
can be given unique names.
Before the MDM can be part of the cluster, it must be promoted to a Standby
MDM.
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Standby MDM and Tie Breaker
An MDM and a Tie Breaker can be added to a system as a standby. Once added,
the standby MDM or Tie Breaker is attached, or locked, to that specific system.
A standby MDM can be called on to assume the position of a Manager MDM or Tie
Breaker MDM when it is promoted to be a cluster member.
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Manager MDM
An MDM that can act as a Master or a Slave in the cluster. Manager MDMs have a
unique system ID, and can be given unique names. A manager can be a standby or
a member of the cluster.
In VxFlex OS documentation, “MDM” refers to a manager, unless specified
otherwise.
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Tie Breaker MDM
An MDM whose sole role is to help determine which MDM is the master. A Tie
Breaker can be a standby or a member of the cluster. A Tie Breaker MDM is not a
manager.
In a 3-node cluster, there is one TB; in a 5-node cluster, there are two TBs. This
ensures that there are always an odd number of MDMs in a cluster, which
guarantees that there is always a majority in electing the master.
The following terms are relevant to the MDM cluster, specifically:
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Master MDM (previously called Primary MDM)
The MDM in the cluster that controls the SDSs and SDCs. The Master MDM
contains and updates the MDM repository, the database that stores the SDS
configuration, and how data is distributed between the SDSs in the system. This
repository is constantly replicated to the Slave MDMs, so they can take over with
no delay.
Every MDM cluster has one Master MDM.
Architecture
Dell EMC VxFlex Ready Node AMS User Guide 27