I/O Data Path Protection

data path protection to a redundant in a is accomplished with the feature and the driver in the Windows operating system (OS), in the Linux OS, and Multi-Plexed I/O (MPxIO) in the Solaris OS.

ADT is a built-in feature of the controller that permits ownership of a logical drive to be transferred to a second controller if the preferred controller fails. When you use ADT with a multi-path driver, ADT helps to make sure that an I/O data path always is available for the in the storage subsystem.

If a component, such as a controller, a cable, or an , fails, or an error occurs on the data path to the preferred controller, ADT and the multi-path driver automatically transfer the and logical drives to the alternate “non-preferred” controller for processing. This failure or error is called a .

Multi-path drivers, such as MPIO, RDAC, and MPxIO, are installed on host computers that access the storage subsystem and provide I/O path failover. The ADT feature is used specifically for single-port cluster failover. The ADT feature mode is automatically selected by the host type.

During a failover, the logical drive transfer is logged as a critical event. You can configure the alert destinations for the storage subsystem to send an alert notification automatically.

Multi-Path Driver with ADT Enabled

Enabling ADT in your storage subsystem and using it with a host multi-path driver helps to make sure that an I/O data path is always available for the storage subsystem logical drives.

When you create a logical drive in a storage subsystem where ADT is enabled, a controller must be assigned to own the logical drive, called the . 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 request to fail, the multi-path driver sends the I/O to the alternate controller.


Important:

You should have the multi-path driver installed at all times. You should always enable the ADT mode. Set the ADT mode to a single port cluster host type.

After the I/O data path problem is corrected, the preferred controller automatically re-establishes ownership of the logical drive as soon as the multi-path driver detects that the path is normal again.

Multi-Path Driver with ADT Disabled

When you disable ADT in your storage subsystem, the I/O data path is still protected as long as a multi-path driver is installed on each host that is connected to the storage subsystem. However, when an I/O request is sent to a specified logical drive, and a problem occurs along the data path to its preferred controller, all logical drives on the preferred controller are transferred to the alternate controller, not just the specified logical drive.