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Important:
You must uninstall the multi-path driver for Dynamic Multi-Pathing (DMP) to become the default multi-path driver.A multi-path driver is a driver, such as RDAC, that can access the storage subsystem over multiple I/O paths. The driver can recover from path failures by using the remaining paths. This operation is known as failover. VERITAS Volume Manager with DMP is another example of a multi-path driver. This multi-path driver requires Array Support Library (ASL) software. The ASL software provides information to the VERITAS Volume Manager for setting up the path associations for the driver.
ADT is a built-in feature of the controller that allows -level failover rather than controller-level failover. ADT is disabled by default. ADT is automatically enabled based on the failover options supported by the that you have specified.
The storage management software has defined behavior for the following configurations, based on host type.
Note:
If you want to change the default ADT settings without changing the host type, contact a representative.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 ). The controller also controls 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 issues the I/O to the alternate controller.
When ADT is enabled and used with a host multi-path driver, ADT helps to make sure that 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.
After the I/O data path problem is corrected, the preferred controller automatically reestablishes ownership of the logical drive as soon as the multi-path driver detects that the path is normal again.
When ADT is disabled, the I/O data path is still protected so long as you use a multi-path driver. Sometimes an I/O request is sent to an individual logical drive, and a problem occurs along the data path to its preferred controller. In this case, all logical drives on that controller are transferred to the other controller instead of just that particular logical drive.
Storage subsystems in this scenario have no failover protection. A pair of active controllers might still be located in a storage subsystem. Each logical drive on the storage subsystem might be assigned a preferred owner. However, logical drives are not allowed to move to the alternate controller.
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. You must manually switch logical drives to the alternate controller in the pair.
Hosts using operating systems without failover capability should be connected to the storage subsystem so each host has only one path to the logical drive.