I/O groups

A pair of nodes is known as an input/output (I/O) group. Depending on the model of your system, either one I/O group or two I/O groups can be configured.

Volumes are logical disks that are presented to the SAN by nodes. Volumes are also associated with the I/O group.

When an application server processes I/O to a volume, it can access the volume with either of the nodes in the I/O group. When you create a volume, you can specify a preferred node. Many of the multipathing driver implementations that the system supports use this information to direct I/O to the preferred node. The other node in the I/O group is used only if the preferred node is not accessible.

If you do not specify a preferred node for a volume, the system selects the node in the I/O group that has the fewest volumes to be the preferred node.

After the preferred node is chosen, it can be changed only when the volume is moved to a different I/O group.

Note: The management GUI provides a wizard that moves volumes between I/O groups without disrupting host I/O operations.
Parent topic: System
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