About Csm Nodes; About Clusters; Physical Topology; Chapter 3 Creating And Managing Cluster - Cisco MDS 9216 Configuration Manual

About CSM Nodes

About CSM Nodes

A node provides virtualization, caching, migration and copy services to the SAN. Nodes are deployed
in pairs with each pair of nodes forming an I/O group. The nodes belonging to the same I/O group MUST
have different power domains. This entails that nodes of the same I/O group should come from two
different CSMs. When a node fails within an I/O group then the other node in the I/O group will take
over the responsibilities of the failed node. Data loss during a node failure is prevented by mirroring the
IO read/write cache info across both the nodes in the I/O group.

About Clusters

Nodes are grouped into clusters of up to 2 pairs of nodes. These nodes are managed as a set (cluster),
and present a single point of control for the user for configuration and service activity. For I/O purposes,
so as to avoid a single point of loss of availability nodes will be grouped into pairs (I/O groups), with a
single pair being responsible for serving I/O on a given VDisk. I/O traffic for a particular VDisk is, at
any one time, handled exclusively by the nodes in a single I/O group. Thus, although a cluster may have
many nodes within it, the nodes handle i/o in independent pairs. This means that the i/o capability of a
cluster scales well, since additional throughput can simply be obtained by adding additional I/O Groups.
There are some circumstances when all the nodes in the cluster do act together rather than in pairs. At
any one time, a single node in the cluster is used to manage configuration activity. The node at which
the cluster got created will start off as the configuration node. This configuration node manages a cache
of the configuration information that describes the cluster configuration and provides a focal point for
configuration commands. Similarly, at any one time, a single node acts as the managing node for overall
management of the cluster. If the configuration node or managing node fails, another node in the cluster
will take over their responsibilities. The nodes also act together to implement the data migration function
described in
There are several advantages to managing a set of nodes as a cluster.
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Physical Topology

In Figure
identified as interface svc 3/1 and interface svc 3/2. CSM 7 has two nodes identified as interface svc
7/1 and interface svc 7/2. These four interfaces are configured to form a 4-node cluster.
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These two I/O groups form a SVC cluster. So SVC interfaces 3/1, 3/2, 7/1, and 7/2 belong to one cluster
Figure 3-1
example in the following sections to understand SVC configurations.
Cisco MDS 9000 Family SAN Volume Controller Configuration Guide
3-2
Chapter 7, "Configuring Copy Services."
All the cluster related configuration operations happen on the config node.
Individual node operations like node addition, deletion, shutdown, can be done at the config node.
All the nodes in the cluster run the same software version. Software upgrade can be initiated for the
whole cluster instead of having to do this on a per-node basis.
3-1, CSMs reside in slots 3 and 7 in a Cisco MDS 9500 Series switch. CSM 3 has two nodes
I/O group 1 includes interface svc 3/1 (Node1) and interface svc 7/1 (Node3).
I/O group 2 is made up of interface svc 3/2 (Node 2) and interface svc 7/2 (Node 4).
also shows two hosts and a back-end storage device. This physical topology serves as an
Chapter 3 Creating and Managing Clusters
78-16119-01, Cisco MDS SAN-OS Release 1.3