For example, a user is given access to internal LUNs 5, 6, and 7, which are mapped to external LUNs 0, 1, and 2, respectively. controller 1 owns LUNs 0 and 1 while controller 2 owns LUN 2. The user is physically connected to controller 1, thus, they will only see LUNs 0 and 1. The user will not be able to access LUN 2. If the user was physically connected to controller Unit 2, the reverse would be true: only LUN 2 would be accessible. When a controller fails, the user will be given access to all mapped LUNs regardless of the physical connection.
Data cache is not copied from one controller to another. If a controller fails, all “dirty” data in cache will be lost. Thus if power failures are a concern, writeback cache should be disabled.
DUAL COHERENCY=ONOFF enables/disables the cache coherency function. Default is dual coherency disabled which is the
DUAL TIMEOUT=X allows you to set the cache coherency timeout for cache node requests in seconds. Valid range is <0...255>. Default is zero (0) seconds. The timeout value should be less than the host timeout value (HOST TIMEOUT=X). A timeout value of 0 allows for only one retry.
NOTE : In dual mode, LUNs will be “owned” by the controller unit on which they are created. Hosts will only see the LUNs on the controller to which they are connected, unless cache coherency is enabled.
3.2.12.2Fail / Restore the Other Controller Unit in the Couplet Pair
To fail the other controller unit in the system (for example, in order to perform maintenance), enter:
dual fail <Enter>
The healthy controller unit will take ownership of all the LUNs/tiers from the failed controller unit.
To restore the other controller unit in the system to healthy status after failure recovery, enter:
dual heal <Enter>
Ownership of LUNs/tiers are transferred back to the formerly failed controller unit.
3.2.12.3Labeling the Controller Unit(s)
You may change the label assigned to each controller unit. This allows you to uniquely identify each unit in the controller system. The CLI prompt for each controller is built by adding a colon (:) and a space at the end of the label. Each controller can have a label up to 31 characters long.
To change the label:
1.Type: dual label=12 <Enter>.
2.Select which unit you want to rename (Figure
3.When prompted, type in the new label for the selected unit. The new name is displayed.
NOTE : If you type DEFAULT for the new label, the label for the unit is restored to its default setting.
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