Configuring Automatic Failback for Multipathing Support

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Symmetrical devices can provide automatic failback to a possible optimal path. If a failover occurs on the initial path, the standby path becomes the new online path. Usually the standby path is a suboptimal path. When automatic failback is enabled, the initial path comes back online and failover to the initial path automatically occurs.

How to Configure Automatic Failback for Specific Multipathing Support

Become an administrator.

Display the supported multipath driver information.

# mpathadm list mpath-support
mpath-support: libmpscsi_vhci.so

Enable automatic failback support for the supported multipath driver.
```
# mpathadm modify mpath-support -a on libmpscsi_vhci.so
 
```

Confirm the configuration change.

# mpathadm show mpath-support libmpscsi_vhci.so
mpath-support:  libmpscsi_vhci.so
        Vendor:  Sun Microsystems
        Driver Name:  scsi_vhci
        Default Load Balance:  round-robin
        Supported Load Balance Types:  
                round-robin
                logical-block
        Allows To Activate Target Port Group Access:  yes
        Allows Path Override:  no
        Supported Auto Failback Config:  1
        Auto Failback:  on
        Failback Polling Rate (current/max):  0/0
        Supported Auto Probing Config:  0
        Auto Probing:  NA
        Probing Polling Rate (current/max):  NA/NA
        Supported Devices:
                Vendor:  SUN     
                Product:  T300            
                Revision:  
                Supported Load Balance Types:
                        round-robin

                Vendor:  SUN     
                Product:  T4              
                Revision:  
                Supported Load Balance Types:
                        round-robin
.
.
.

Note - The automatic display initiated by the mpathadm modify command setting is effective while the system is running. However, to keep the changed setting persistent, you must update the /etc/driver/drv/scsi_vhci.conf file. Refer to Configuring Automatic Failback.

How to Fail Over a LU

This operation is applicable only to devices in 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 libmpscsi_vhci.so and providing explicit mode asymmetric LU access

Display a list of multipathed LUs.

# mpathadm list lu
        /dev/rdsk/c0t600144F08069703400004E828EE10004d0s2
                Total Path Count: 8
                Operational Path Count: 8
        /dev/rdsk/c0t600144F08069703400004E8183DF0002d0s2
                Total Path Count: 8
                Operational Path Count: 8
        /dev/rdsk/c0t600A0B800026D63A0000A4994E2342D4d0s2
                Total Path Count: 4
                Operational Path Count: 4
        /dev/rdsk/c0t600A0B800029065C00007CF54E234013d0s2
                Total Path Count: 4
                Operational Path Count: 4
        /dev/rdsk/c0t600A0B800026D63A0000A4984E234298d0s2
                Total Path Count: 4
                Operational Path Count: 4
.
.
.

Display a specific LU's configuration information.

# mpathadm show lu /dev/rdsk/c0t600A0B800026D63A0000A4984E234298d0s2
Logical Unit:  /dev/rdsk/c0t600A0B800026D63A0000A4984E234298d0s2
        mpath-support:  libmpscsi_vhci.so
        Vendor:  SUN     
        Product:  CSM200_R        
        Revision:  0660
        Name Type:  unknown type
        Name:  600a0b800026d63a0000a4984e234298
        Asymmetric:  yes
        Current Load Balance:  round-robin
        Logical Unit Group ID:  NA
        Auto Failback:  on
        Auto Probing:  NA

        Paths:  
                Initiator Port Name:  210000e08b841feb
                Target Port Name:  200800a0b826d63b
                Override Path:  NA
                Path State:  OK
                Disabled:  no

                Initiator Port Name:  210000e08b841feb
                Target Port Name:  200900a0b826d63b
                Override Path:  NA
                Path State:  OK
                Disabled:  no

                Initiator Port Name:  210000e08b841feb
                Target Port Name:  200800a0b826d63c
                Override Path:  NA
                Path State:  OK
                Disabled:  no

                Initiator Port Name:  210000e08b841feb
                Target Port Name:  200900a0b826d63c
                Override Path:  NA
                Path State:  OK
                Disabled:  no

        Target Port Groups:  
                ID:  5
                Explicit Failover:  yes
                Access State:  active
                Target Ports:
                        Name:  200800a0b826d63b
                        Relative ID:  0

                        Name:  200800a0b826d63c
                        Relative ID:  0

                ID:  15
                Explicit Failover:  yes
                Access State:  standby
                Target Ports:
                        Name:  200900a0b826d63b
                        Relative ID:  0

                        Name:  200900a0b826d63c
                        Relative ID:  0

Manually force a LU failover.
```
# mpathadm failover lu /dev/rdsk/c0t600A0B800026D63A0000A4984E234298d0s2
```
If this operation is successful, the access state of the device's target port groups changes as a result of the logical unit failover.

Confirm the access state change.

# mpathadm show lu /dev/rdsk/c0t600A0B800026D63A0000A4984E234298d0s2
Logical Unit:  /dev/rdsk/c0t600A0B800026D63A0000A4984E234298d0s2
        mpath-support:  libmpscsi_vhci.so
        Vendor:  SUN     
        Product:  CSM200_R        
        Revision:  0660
        Name Type:  unknown type
        Name:  600a0b800026d63a0000a4984e234298
        Asymmetric:  yes
        Current Load Balance:  round-robin
        Logical Unit Group ID:  NA
        Auto Failback:  on
        Auto Probing:  NA

        Paths:  
                Initiator Port Name:  210000e08b841feb
                Target Port Name:  200800a0b826d63b
                Override Path:  NA
                Path State:  OK
                Disabled:  no

                Initiator Port Name:  210000e08b841feb
                Target Port Name:  200900a0b826d63b
                Override Path:  NA
                Path State:  OK
                Disabled:  no

                Initiator Port Name:  210000e08b841feb
                Target Port Name:  200800a0b826d63c
                Override Path:  NA
                Path State:  OK
                Disabled:  no

                Initiator Port Name:  210000e08b841feb
                Target Port Name:  200900a0b826d63c
                Override Path:  NA
                Path State:  OK
                Disabled:  no

        Target Port Groups:  
                ID:  5
                Explicit Failover:  yes
                Access State:  standby
                Target Ports:
                        Name:  200800a0b826d63b
                        Relative ID:  0

                        Name:  200800a0b826d63c
                        Relative ID:  0

                ID:  15
                Explicit Failover:  yes
                Access State:  active
                Target Ports:
                        Name:  200900a0b826d63b
                        Relative ID:  0

                        Name:  200900a0b826d63c
                        Relative ID:  0

How to Enable a LU Path

If the path to a LU is disabled, the enable command changes the path back to enabled. The full path must be specified using the initiator port name, target port name, and the LU. To verify the change, run the show command for the logical unit.

Display a list of multipathed LUs.

# mpathadm list lu
        /dev/rdsk/c0t600144F08069703400004E828EE10004d0s2
                Total Path Count: 8
                Operational Path Count: 8
        /dev/rdsk/c0t600144F08069703400004E8183DF0002d0s2
                Total Path Count: 8
                Operational Path Count: 8
        /dev/rdsk/c0t600A0B800026D63A0000A4994E2342D4d0s2
                Total Path Count: 4
                Operational Path Count: 4
        /dev/rdsk/c0t600A0B800029065C00007CF54E234013d0s2
                Total Path Count: 4
                Operational Path Count: 4
        /dev/rdsk/c0t600A0B800026D63A0000A4984E234298d0s2
                Total Path Count: 4
                Operational Path Count: 4
        /dev/rdsk/c0t600A0B800029065C00007CF44E233FCFd0s2
                Total Path Count: 4
                Operational Path Count: 4
.
.
.

Display the selected LU's configuration information.

# mpathadm show lu 
Logical Unit:  /dev/rdsk/c0t600A0B800026D63A0000A4984E234298d0s2
        mpath-support:  libmpscsi_vhci.so
        Vendor:  SUN     
        Product:  CSM200_R        
        Revision:  0660
        Name Type:  unknown type
        Name:  600a0b800026d63a0000a4984e234298
        Asymmetric:  yes
        Current Load Balance:  round-robin
        Logical Unit Group ID:  NA
        Auto Failback:  on
        Auto Probing:  NA

        Paths:  
                Initiator Port Name:  210000e08b841feb
                Target Port Name:  200800a0b826d63b
                Override Path:  NA
                Path State:  OK
                Disabled:  no

                Initiator Port Name:  210000e08b841feb
                Target Port Name:  200900a0b826d63b
                Override Path:  NA
                Path State:  OK
                Disabled:  no

                Initiator Port Name:  210000e08b841feb
                Target Port Name:  200800a0b826d63c
                Override Path:  NA
                Path State:  OK
                Disabled:  no

                Initiator Port Name:  210000e08b841feb
                Target Port Name:  200900a0b826d63c
                Override Path:  NA
                Path State:  OK
                Disabled:  no

        Target Port Groups:  
                ID:  5
                Explicit Failover:  yes
                Access State:  standby
                Target Ports:
                        Name:  200800a0b826d63b
                        Relative ID:  0

                        Name:  200800a0b826d63c
                        Relative ID:  0

                ID:  15
                Explicit Failover:  yes
                Access State:  active
                Target Ports:
                        Name:  200900a0b826d63b
                        Relative ID:  0

                        Name:  200900a0b826d63c
                        Relative ID:  0

Enable the LU path.

# mpathadm enable path -i 210000e08b841feb -t 200900a0b826d63b \ 
           -l /dev/rdsk/c0t600A0B800026D63A0000A4984E234298d0s2

How to Disable a LU Path

This operation disables the LU path, regardless of its operational state.

Note - The disabled state is not persistent across rebooting. If the path is operational before the next boot sequence, it is enabled by default. This operation is not allowed when the given path is the last operational path remaining.

Display a list of multipathed LUs.

# mpathadm list lu
        /dev/rdsk/c0t600144F08069703400004E828EE10004d0s2
                Total Path Count: 8
                Operational Path Count: 8
        /dev/rdsk/c0t600144F08069703400004E8183DF0002d0s2
                Total Path Count: 8
                Operational Path Count: 8
        /dev/rdsk/c0t600A0B800026D63A0000A4994E2342D4d0s2
                Total Path Count: 4
                Operational Path Count: 4
        /dev/rdsk/c0t600A0B800029065C00007CF54E234013d0s2
                Total Path Count: 4
                Operational Path Count: 4
        /dev/rdsk/c0t600A0B800026D63A0000A4984E234298d0s2
                Total Path Count: 4
                Operational Path Count: 4
        /dev/rdsk/c0t600A0B800029065C00007CF44E233FCFd0s2
                Total Path Count: 4
                Operational Path Count: 4
.
.
.

Display the specific LU's configuration information.

# mpathadm show lu /dev/rdsk/c0t600A0B800029065C00007CF34E233F89d0s2
Logical Unit:  /dev/rdsk/c0t600A0B800029065C00007CF34E233F89d0s2
        mpath-support:  libmpscsi_vhci.so
        Vendor:  SUN     
        Product:  CSM200_R        
        Revision:  0660
        Name Type:  unknown type
        Name:  600a0b800029065c00007cf34e233f89
        Asymmetric:  yes
        Current Load Balance:  round-robin
        Logical Unit Group ID:  NA
        Auto Failback:  on
        Auto Probing:  NA

        Paths:  
                Initiator Port Name:  210000e08b841feb
                Target Port Name:  200800a0b826d63b
                Override Path:  NA
                Path State:  OK
                Disabled:  no

                Initiator Port Name:  210000e08b841feb
                Target Port Name:  200900a0b826d63b
                Override Path:  NA
                Path State:  OK
                Disabled:  no

                Initiator Port Name:  210000e08b841feb
                Target Port Name:  200800a0b826d63c
                Override Path:  NA
                Path State:  OK
                Disabled:  no

                Initiator Port Name:  210000e08b841feb
                Target Port Name:  200900a0b826d63c
                Override Path:  NA
                Path State:  OK
                Disabled:  no

        Target Port Groups:  
                ID:  8
                Explicit Failover:  yes
                Access State:  standby
                Target Ports:
                        Name:  200800a0b826d63b
                        Relative ID:  0

                        Name:  200800a0b826d63c
                        Relative ID:  0

                ID:  18
                Explicit Failover:  yes
                Access State:  active
                Target Ports:
                        Name:  200900a0b826d63b
                        Relative ID:  0

                        Name:  200900a0b826d63c
                        Relative ID:  0

Select an initiator port and a target port name.

Disable the selected LU path.

# mpathadm disable path -i 210000e08b841feb -t 200900a0b826d63b \
           -l /dev/rdsk/c0t600A0B800029065C00007CF34E233F89d0s2