Product manual

Galaxy G3G12 / G3G16 - Installation and Hardware Reference Manual
232 Section 7 Technology Background
7.6 LUN Affinity
Galaxy3G Fibre Channel subsystems with two controllers include a LUN Affinity feature. Normally, either
controller can access all logical drives. LUN Affinity enables you to specify which controller can access each
logical drive. Use this feature to balance the load of your logical drives between the two controllers.
To use LUN Affinity you must:
• Have two controllers in the subsystem
• Enable LUN Affinity under controller settings.
Disk Array Creation
When you create a logical drive using the Advanced method of disk array creation, you can specify the
Preferred Controller ID:
• Controller 1 – Assign all logical drives to Controller 1
• Controller 2 – Assign all logical drives to Controller 2
• Automatic – Alternate logical drive assignments between Controllers 1 and 2
Automatic is the default and preferred setting because it will balance the logical drive assignments for you.
When you create a logical drive using the Automatic or Express disk array creation, the logical drives are
assigned alternatively between Controllers 1 and 2 automatically.
See “Creating a Disk Array – Automatic” , “Creating a Disk Array – Express” , or “Creating a Disk Array –
Advanced” .
Logical Drive Settings
After you have created a logical drive, you can click on the Settings tab and manually change the Preferred
Controller ID between Controller 1 and Controller 2. See “Making Logical Drive Settings”.
If you create logical drives with LUN Affinity disabled, the Preferred Controller ID will show N/A, and your
logical drives will be visible to both controllers.
If you create logical drives with LUN Affinity disabled, and later you enable LUN Affinity, all of your logical
drives will be assigned to Controller 1. To balance the load, you can reassign some of your logical drives to
Controller 2 under the Preferred Controller ID in the Settings tab. See “Making Logical Drive Settings”.
When you a delete a logical drive, the remaining logical drives keep the same Controller assignments. If you
want to rebalance controller assignments of the remaining logical drives, change their Preferred Controller
IDs in the Settings tab.
Failover and Failback
When one controller fails, the surviving controller takes over logical drive access until the failed controller is
brought back online or is replaced. For example, LUN Affinity is enabled and your logical drives are
assigned to Controller 1. The following actions will happen:
• If Controller 1 goes offline, Controller 2 takes over access to the logical drives assigned to Controller 1.
• If Controller 1 comes back online, Controller 1 takes back access to the logical drives assigned to it.
• If Controller 1 is replaced, the new controller takes over access to the logical drives assigned to
Controller 1.
• All logical drives assigned to Controller 2 remain accessible by Controller 2. Controller 1 cannot access
them at any time.