Product manual

Chapter 7: Technology Background
249
• If Controller 1 goes offline, Controller 2 takes over access to the logical
drives assigned to Controller 1.
• All write data that is still in the controller cache will be written to the logical
drives, even though the controller managing them has failed.
• 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.
LUN Affinity
VTrak 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. See page 107 or page 156
On subsystems with two controllers, when Cache Mirroring is disabled, LUN
Affinity is enabled automatically. See “Cache Mirroring” on page 248.
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” on page 122, “Creating a Disk Array –
Express” on page 122, or “Creating a Disk Array – Advanced” on page 123.