Planning: MD3200i Series Storage Array Terms and Concepts 55
The multi-path software identifies the existence of multiple paths to a virtual
disk and establishes a preferred path to that disk. If any component in the
preferred path fails, the multi-path software automatically re-routes I/O
requests to the alternate path so that the storage array continues to operate
without interruption.
NOTE: Multi-path software available on the MD3200i series resource media.
Preferred and Alternate Controllers and Paths
A preferred controller is a RAID controller module designated as the owner of
a virtual disk or disk group. The preferred controller is automatically selected
by MDSM when a virtual disk is created. You can change the preferred RAID
controller module owner of a virtual disk after it is created. If a host is only
connected to only one RAID controller module, the preferred owner must
manually be assigned to the RAID controller module the host can access.
Ownership of a virtual disk is moved from the preferred controller to the
secondary controller (also called the alternate controller) when the preferred
controller is:
• Physically removed
• Updating firmware
• Involved in an event that caused failover to the alternate controller
Paths used by the preferred RAID controller module to access either the disks
or the host server are called the preferred paths; redundant paths are called
the alternate paths. If a failure causes the preferred path to become
inaccessible, the storage array automatically uses the alternate path to access
data. When this occurs the enclosure status LED blinks amber.
Virtual Disk Ownership
MDSM can be used to automatically build and view virtual disks. It uses
optimal settings to stripe the disk group. Virtual disks are assigned to
alternating RAID controller modules when they are created. This default
assignation provides a simple means for load balancing the workload of the
RAID controller modules.
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