User Manual

Advanced Functions
5-20
• Owner controller and preferred controller
The controller implements the ALUA (Asymmetric Logical Unit Access)
algorithm to ensure that only one controller is allowed to access a virtual
disk. The controller that controls a virtual disk is the owner controller of the
virtual disk. When both controllers are healthy and all paths are online, the
owner controller is the same as the preferred controller. There are two
possible cases that the preferred controller loses the ownership of a virtual
disk to the peer controller:
1. If a controller fails, the survival controller will take over the ownership of
all virtual disks of the faulty controller.
2. When all the paths to a controller are disconnected, the MPIO driver
will force the virtual disks to transfer to the other controller.
The preferred controller is specified when a virtual disk is created, and it
can be changed later by users (see the Preferred Controller option in
Section 2.6.2, 2.6. 4, and 2.6.5 for modifying JBOD disk, logical disk, and
volume, respectively). But the owner controller is changed dynamically
according to the current path and controller status.
• Single-controller mode in redundant-controller system
If a redundant-controller RAID system is powered up with only one
controller installed, the system will be operating in the single-controller
mode, and there is no event or beeper alert because of the absence of
the peer controller. But if the other controller is installed, the system will be
operating in redundant-controller mode.
While enabling the mirror write cache protects the data integrity,
disabling this option may cause data loss when the controller is failover
but allows better write performance. For the purpose of data protection,
it is suggested to turn this option on.
5.3.2 Controller Data Synchronization
When running in a redundant environment, two controllers will
automatically synchronize the configuration data, event logs, task
progress data, system time, and firmware. See further details as described
below.
Note
To get best performance, make all LDs in a DG have the same
preferred controller, and evenly distribute DGs between the two
controllers.
Note
Once the a virtual disk has been exported to host as a LUN on a
controller, the owner controller can be changed only after restart the
controller, and the Change owner controller immediately option is not
displayed.