Failover of a Logical Unit

Language:

You can failover a logical unit (LU) in a device, which belongs to one of the following two categories:

Asymmetric devices with a proprietary failover mechanism recognized and supported by multipathing support.
Devices conforming to the T10 standard Target Port Group Support (TPGS) and providing explicit mode ALUA.

How to Failover a Logical Unit

Display the configuration information of a specific logical unit.

# mpathadm show lu  /dev/rdsk/c0t600144F0DDA8BB1A000057208C880001d0s2                                  
Logical Unit:  /dev/rdsk/c0t600144F0DDA8BB1A000057208C880001d0s2
        mpath-support:  libmpscsi_vhci.so
        Vendor:  SUN     
        Product:  ZFS Storage 7420
        Revision:  1.0 
        Name Type:  unknown type
        Name:  600144f0dda8bb1a000057208c880001
        Asymmetric:  yes
        Current Load Balance:  shortest-path
        Logical Unit Group ID:  NA
        Auto Failback:  on
        Auto Probing:  NA

        Paths:  
                Initiator Port Name:  iqn.1986-03.com.sun:01:21866c42ab36.5710b544,4000002a00ff
                Target Port Name:  4000002a0000,iqn.1986-03.com.sun:02:56bf24c4-e3e3-4ff0-e7b0-a6e6880e461d
                Override Path:  NA
                Path State:  OK
                Disabled:  no

        Target Port Groups:  
                ID:  0
                Explicit Failover:  no
                Access State:  active optimized
                Target Ports:
                        Name:  4000002a0000,iqn.1986-03.com.sun:02:56bf24c4-e3e3-4ff0-e7b0-a6e6880e461d
                        Relative ID:  3

You can check the current access state of the Target Port Groups in the output. To ensure that the storage device supports explicit failover, you must verify that the value of Explicit Failover in the output is yes.

Manually force a logical unit failover.
```
# mpathadm failover lu /dev/rdsk/c0t600144F0DDA8BB1A000057208C880001d0s2
```
If this operation is successful, the access state of the Target Port Groups of the device changes as a result of the logical unit failover.

Confirm the access state change.

# mpathadm show lu  /dev/rdsk/c0t600144F0DDA8BB1A000057208C880001d0s2
Logical Unit:  /dev/rdsk/c0t600144F0DDA8BB1A000057208C880001d0s2
        mpath-support:  libmpscsi_vhci.so
        Vendor:  SUN     
        Product:  ZFS Storage 7420
        Revision:  1.0 
        Name Type:  unknown type
        Name:  600144f0dda8bb1a000057208c880001
        Asymmetric:  yes
        Current Load Balance:  shortest-path
        Logical Unit Group ID:  NA
        Auto Failback:  on
        Auto Probing:  NA

        Paths:  
                Initiator Port Name:  iqn.1986-03.com.sun:01:21866c42ab36.5710b544,4000002a00ff
                Target Port Name:  4000002a0000,iqn.1986-03.com.sun:02:56bf24c4-e3e3-4ff0-e7b0-a6e6880e461d
                Override Path:  NA
                Path State:  OK
                Disabled:  no

        Target Port Groups:  
                ID:  0
                Explicit Failover:  yes
                Access State:  active optimized
                Target Ports:
                        Name:  4000002a0000,iqn.1986-03.com.sun:02:56bf24c4-e3e3-4ff0-e7b0-a6e6880e461d
                        Relative ID:  3