Planning: MD3200i Series Storage Array Terms and Concepts 55
• 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.
Ownership can later be modified to balance workload according to actual
usage. If virtual disk ownership is not manually balanced, it is possible for one
controller to have the majority of the work, while the other controller is idle.
Limit the number of virtual disks in a disk group. If multiple virtual disks are
in a disk group, consider:
• The impact each virtual disk has on other virtual disks in the same disk
group.
• The patterns of usage for each virtual disk.
• Different virtual disks have higher usage at different times of day.
Load Balancing
A load balance policy is used to determine which path is used to process I/O.
Multiple options for setting the load balance policies lets you optimize I/O
performance when mixed host interfaces are configured.
You can choose one of these load balance policies to optimize I/O
performance:
• Round robin with subset—The round robin with subset I/O load balance
policy routes I/O requests, in rotation, to each available data path to the
RAID controller module that owns the virtual disks. This policy treats all
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