Configuring and Unconfiguring Path Failover Support

Control path failover support is not enabled automatically when the device driver is installed. The Linux lin_tape device driver provides a driver parameter

alternate_pathing for you to enable the library control path failover. To enable the failover support in the lin_tape device driver software, you need do the following steps after installing the lin_tape rpm package:

1. lin_taped stop (stop the lin_taped daemon)

2. rmmod lin_tape (unload the lin_tape driver from the memory)

3. Add the following line in your/etc/modules.conffile for 2.4 kernels or /etc/modprobe.conf.local file for 2.6 kernels:

optionslin_tape alternate_pathing=1

4. depmod

5. modprobe lin_tape (re-load the lin_tape driver into memory)

6. lin_taped (re-start lin_taped daemon)

You can ignore the″Unresolved symbols in/lib/modules/<your kernel

name>/drivers/scsi/lin_tape.ko″message after the″depmod″command. You can check if the lin_tape driver has recognized multiple control paths for your library by reading the /proc/scsi/IBMchanger file.

v _{cat/proc/scsi/IBMchanger}

If your library lists ″Primary″or″Alternate″under″FO Path″, you have successfully enabled control path failover feature for your library. If it is″NA″ listed under ″FO Path″, then the control path failover is not enabled. After control path failover support is enabled, it remains set until the lin_tape driver is reloaded with the alternate_pathing driver parameter set to OFF . The path failover setting is retained even if the system is rebooted. If you want to turn off the control path failover feature in the lin_tape device driver, you can perform the following steps:

1. lin_taped stop

2. rmmod lin_tape

3. Delete the following line in your/etc/modules.conffile: options lin_tape alternate_pathing=1

4. depmod

5. modprobe lin_tape

6. lin_taped

Primary and Alternate Paths

When lin_tape is loaded into kernel memory, the first logical medium changer device that lin_tape sees in the system is the primary path for that medium

changer. The other logical medium changers that lin_tape attached for the same medium changer are configured as alternate paths. The device driver supports up to 16 physical paths for a single device. The primary and alternate path

information can be obtained by the following command: v _{cat /proc/scsi/IBMchanger}

The following is an example of a /proc/scsi/IBMchanger file: v _{lin_tape version: 3.0.3}

v _{lin_tape major number: 253}

Attached Changer Devices:

Number Model SN HBA FO Path

0 03584L22 IBM1234567 qla2xxx Primary

1 03584L22 IBM1234567 qla2xxx Alternate

2 03584L22 IBM1234567 qla2xxx Alternate

The labeling of a logical device as either a primary or alternate path is for information only, in order to:

v _{Be able to identify the actual number of physical devices configured on the} system and a specific logical device associated with them. There is only one logical device labeled as the primary path for each physical device. However, there can be multiple logical devices labeled as an alternate path for the same devices.

v _{Provide information about which logical devices configured on the system have} path failover support enabled.

Querying Primary and Alternate Path Configuration

You can display the primary and alternate path configuration for all devices by reading the/proc/scsi/IBMchanger file, as explained in section “Primary and Alternate Paths” on page 108.

Note: Display the primary and alternate path configuration for any device using tape diagnostic and utility functions, refer to Chapter 10, “IBM Tape Diagnostic Tool (ITDT),” on page 259 or “Linux System - Tape Utility Program (IBMtapeutil)” on page 385.

Disable and Enable Primary and Alternate Paths

Once you load the lin_tape device driver with the alternate_pathingparameter to be ON, by default, all the available paths for a physical device are enabled.

If it is necessary to disable a path and not perform path fail over (for example due to maintenance), run commands to disable and then later enable the primary and alternate paths.

The commands to enable and disable primary and alternate paths are tape diagnostic and utility functions.

Note: See Chapter 10, “IBM Tape Diagnostic Tool (ITDT),” on page 259 or “Linux System - Tape Utility Program (IBMtapeutil)” on page 385

Data Path Failover and Load Balancing Support for Tape Drives

Data path failover support is not enabled automatically when the device driver is installed. The Linux lin_tape device driver provides a driver parameter

alternate_pathing for you to enable the data path failover.

To enable the failover support in the lin_tape device driver software, you need to perform the following steps after installing the lin_tape rpmpackage.

>lin_taped stop (stop the lin_taped daemon)

>rmmod lin_tape (unload the lin_tape driver from the memory If you have IBM 3592 tape drives, add the following line in your

/etc/modules.conf file for 2.4 kernels or /etc/modprobe.conf.local file for 2.6 kernels:

options lin_tape alternate_pathing=1

If you have IBM LTO tape drives, the library needs to have path failover feature code. The data path failover license keys are needed to enable the failover if you are running LTO2 drives or if you are running LTO3 drives with old levels of drive code. DPF keys do not need to be added if you are running the latest drive code on LTO3 or LTO4 drives.

Add the following line in your /etc/modules.conf file for 2.4 kernels or /etc/modprobe.conf.local file for 2.6 kernels:

options lin_tape alternate_pathing=1 dpf_keys="abcdefghijklmnop"

″abckdefghijklmnop″is an example of a data path failover feature key. If you have multiple libraries and multiple data path failover feature keys, input your keys as follows:

dpf_keys="key1;key2;..."

Save the file, then run the following commands: >depmod

>modprobe lin_tape (re-load the lin_tape driver into memory) >lin_taped (re-start lin_taped daemon)

You may ignore the″Unresolved symbols in /lib/modules/<your kernel

name>/drivers/scsi/lin_tape.ko″message after thedepmodcommand. You can check if the lin_tape driver has recognized multiple paths for your tape drive by reading the/proc/scsi/IBMtapefile:

>cat /proc/scsi/IBMtape

If your tape drive lists ″Primary″or″Alternate″under″FO Path″, you have successfully enabled data path failover feature for your tape drive. If it is″NA″ listed under ″FO Path″, then the data path failover is not enabled. After the path failover support is enabled, it remains set until the lin_tape driver is reloaded with thealternate_pathingdriver parameter set to OFF . The path failover setting is retained even if the system is rebooted. If you want to turn off the data path failover feature in the lin_tape device driver, you may do the following steps: >lin_taped stop

>rmmod lin_tape

Delete the following line in your/etc/modules.conffile: options lin_tape alternate_pathing=1

>depmod

>modprobe lin_tape >lin_taped

Primary and Alternate Paths

When the lin_tape device driver is loaded into kernel memory with path failover support enabled, the first logic device that lin_tape sees always becomes the primary path. The other logical devices that lin_tape sees are configured as the alternate paths. The device driver supports up to 16 physical paths for a single device.

The primary and alternate path information can be obtained by the following command:

>cat /proc/scsi/IBMtape

The following is an example of a /proc/scsi/IBMtape: lin_tape version: 3.0.3

lin_tape major number: 253 Attached Tape Devices:

Number Model SN HBA FO Path

0 03592 IBM1234567 qla2xxx Primary

1 03592 IBM1234567 qla2xxx Alternate

The labeling of a logical device as either a primary or alternate path is for information only to:

v _{Be able to identify the actual number of physical devices configured on the} system and a specific logical device associated with them. There is only one logical device labeled the primary path for each physical device. However, there may be many (multiple) logical devices labeled as an alternate path for the same devices.