Learn About Failover Protection Settings

Related Topics

I/O data path protection to redundant controllers in a storage subsystem is accomplished with the Auto-Logical Drive Transfer (ADT) feature and a host multi-path driver .

A multi-path driver is an I/O path failover driver installed on host computers that access the storage subsystem, such as RDAC (Redundant Disk Array Controller) . ADT is a built-in feature of the controller firmware that allows logical drive-level failover rather than controller-level failover.

ADT is disabled by default and will be automatically enabled based on the failover options supported by the host type you have specified. For operating system-specific failover options, refer to your storage management software installation guide.

The storage management software uses the following default settings, based on host type:

Note: If you want to change the default ADT settings, contact technical support.

Multi-Path Driver with ADT Enabled

A pair of active controllers are located in a storage subsystem. When you create a logical drive, you assign a controller to own the logical drive (called preferred controller ownership ) and to control the I/O between the logical drive and the application host along the I/O path.

The preferred controller normally receives the I/O requests to the logical drive. If a problem along the data path (such as a component failure) causes an I/O to fail, the multi-path driver will issue the I/O to the alternate controller.

When ADT is enabled and used in conjunction with a host multi-path driver, it helps ensure an I/O data path is available for the storage subsystem logical drives. The ADT feature changes the ownership of the logical drive receiving the I/O to the alternate controller.

Once the I/O data path problem is corrected, the preferred controller will automatically reestablish ownership of the logical drive as soon as the multi-path driver detects the path is normal again.

Multi-Path Driver with ADT Disabled

When ADT is disabled, the I/O data path will still be protected as long as you use a multi-path driver. However, when an I/O request is sent to an individual logical drive and a problem occurs along the data path to its preferred controller, all logical drives on that controller will be transferred to the other controller instead of just that particular logical drive.

No Multi-Path Driver with ADT Enabled

Storage Subsystems in this scenario have no failover protection. A pair of active controllers might still be located in a storage subsystem and each logical drive on the storage subsystem might be assigned a preferred owner. However, logical drives will not move to the alternate controller because there is no multi-path driver installed.

When a component in the I/O path fails, such as a cable or the controller itself, I/O cannot get through to the storage subsystem. The component failure must be corrected before I/O can resume. (Switching logical drives to the alternate controller in the pair must be done manually.)

Hosts using operating systems without failover capability should be connected to the storage subsystem so each host adapter has only one path to the controller. For more information refer to your Controller Enclosure, Drive Enclosure, and Storage System Installation Guide.

Related Topics

Changing Controller Ownership of an Array or Logical Drive

Changing a Storage Subsystem's Default Host Type

Redistributing Logical Drives