Learn About Failover Protection Settings

I/O data path protection to redundant  in a  is accomplished with the  feature and a  

Important:  must be uninstalled in order for DMP to become the default multi-path driver.

A multi-path driver is a driver, such as , that can access the storage array over multiple I/O paths and can recover from path failures by using remaining paths. This is known as failover. VERITAS Virtual Disk Manager with Dynamic Multi-Pathing (DMP) is another example of a multi-path driver. This multi-path driver requires Array Support Library (ASL) software, which provides information to the VERITAS Virtual Disk Manager for setting up the path associations for the driver.

AVT is a built-in feature of the RAID controller module  that allows -level failover rather than RAID controller module-level failover. AVT is disabled by default and will be automatically enabled based on the failover options supported by the  you have specified. For operating system-specific failover options, refer to your operating system-specific storage management software installation guide.

The storage management software has defined behavior for the following configurations, based on host type. For details on which operating systems support which type of failover, refer to your Storage System Product Release Notes:

Note: If you want to change the default AVT settings without changing the host type, contact Customer and Technical Support.

Multi-Path Driver with AVT Enabled

A pair of active RAID controller modules are located in a storage array. When you create a virtual disk, you assign a RAID controller module to own the virtual disk (called ) and to control the I/O between the virtual disk and the application host along the I/O path.

The preferred RAID controller module normally receives the I/O requests to the virtual disk. 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 RAID controller module.

When AVT 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 array virtual disks. The AVT feature changes the ownership of the virtual disk receiving the I/O to the alternate RAID controller module.

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

Multi-Path Driver with AVT Disabled

When AVT 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 virtual disk and a problem occurs along the data path to its preferred RAID controller module, all virtual disks on that RAID controller module will be transferred to the other RAID controller module instead of just that particular virtual disk.

No Multi-Path Driver with AVT Disabled

Storage arrays in this scenario have no failover protection. A pair of active RAID controller modules might still be located in a storage array and each virtual disk on the storage array might be assigned a preferred owner. However, virtual disks are not allowed to move to the alternate RAID controller module.

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

Hosts using operating systems without failover capability should be connected to the storage array so each  has only one path to the virtual disk. For more information, refer to your operating system-specific storage management software installation guide .

Related Topics

Changing RAID Controller Module Ownership of a Disk Group or Virtual Disk

Changing a Storage Array's Default Host Type

Redistributing Virtual Disks

Changing the Failover Alert Delay