Connecting direct attach configurations
A dual-controller configuration improves application availability. If a controller failure occurs, the affected controller fails over to the healthy
partner controller with little interruption to data flow.
A failed controller can be replaced without the need to shut down the storage system.
NOTE:
In the following examples, a single diagram represents CNC, SAS, and 10Gbase-T host connections for ME4
Series controller enclosures. The location and sizes of the host ports are similar. Blue cables show controller A paths
and green cables show controller B paths for host connection.
Single-controller module configurations
A single controller module configuration does not provide redundancy if a controller module fails.
This configuration is intended only for environments where high availability is not required. If the controller module fails, the host loses
access to the storage data until failure recovery actions are completed.
NOTE:
Expansion enclosures are not supported in a single controller module configuration.
Figure 19. Connecting hosts: ME4 Series 2U direct attach – one server, one HBA, single path
1. Server
2. Controller module in slot A
3. Controller module blank in slot B
NOTE:
If the ME4 Series 2U controller enclosure is configured with a single controller module, the controller module
must be installed in the upper slot. A controller module blank must be installed in the lower slot. This configuration is
required to enable sufficient air flow through the enclosure during operation.
Dual-controller module configurations
A dual-controller module configuration improves application availability.
If a controller module failure occurs, the affected controller module fails over to the partner controller module with little interruption to
data flow. A failed controller module can be replaced without the need to shut down the storage system.
In a dual-controller module system, hosts use LUN-identifying information from both controller modules to determine the data paths are
available to a volume. Assuming MPIO software is installed, a host can use any available data path to access a volume that is owned by
either controller module. The path providing the best performance is through the host ports on the controller module that owns the
volume . Both controller modules share one set of 1,024 LUNs (0-1,023) for use in mapping volumes to hosts.
Dual-controller module configurations – directly attached
In the following figures, blue cables show controller module A paths, and green cables show controller module B paths for host connection:
Figure 20. Connecting hosts: ME4 Series 2U direct attach – one server, one HBA, dual path
1. Server
2. Controller module in slot A
3. Controller module in slot B
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Cable host servers to the storage system
