Tape Multipath

Allow most Fibre Channel tape and tape library devices to be attached multiple times to the same partition.

With IBM® i 7.2 TR2 and later releases, support is added to allow most Fibre Channel tape and tape library devices to be attached multiple times to the same IBM i partition.

Up to eight paths are supported for each device.
The multipath functions available depends upon the capabilities of the attached tape and tape library devices.
For maximum redundancy, you can use both ports of the tape devices to attach to the partition.
Because tape devices are sequential access devices, only one path to the device can be active at a time.

Multipath support with failover is provided for the following newer technology tape and tape library devices.

Fibre Channel LTO5, LTO6, LTO7, and LTO8 drives in the 7226 enclosure.
TS3100/TS3200 (3573) with LTO5, LTO6, LTO7, and LTO8 Fibre Channel drives.
TS3310 (3576) with LTO5, LTO6, LTO7, and LTO8 Fibre Channel drives.
TS3500/TS4500 with LTO5, LTO6, LTO7, LTO8, 3592-E07, and 3592-E08, 3592-55F, and 3592-60F Fibre Channel drives.
TS3500 with 3592-E05 and 3592-E06 Fibre Channel drives. (requires 7.2 PTF MF64644 or 7.3 PTF MF64645 or 7.4)
ProtecTIER® virtual tape library.

Multipath support with automatic failover

For the newer technology tape and tape library devices and IBM i 7.2 TR3 and later releases, attaching the same device multiple times to different adapters or adapter ports on the same IBM i partition provides a configuration where I/O path failures can be automatically recovered for most types of errors by the system switching the I/O to an alternative path. In the cases where automatic recovery is not possible then the manual failover support added with IBM i 7.2 TR2 can still be used.

Multipath support with manual failover

For the newer technology tape and tape library devices and IBM i 7.2 TR2, attaching the same device multiple times to different adapters or adapter ports on the same IBM i partition provides a configuration where I/O path failures can be recovered by vary off and vary on of the affected device descriptions, or deallocate and allocate of a failing resource within a tape library device to switch to an alternative path.

Multipath tolerance

For most of the older technology tape and tape library devices, attaching the same device multiple times to a different adapter or adapter ports on the same IBM i partition provides a usable configuration that behaves the same as if there was only one path to the device for most operations.

Multipath tolerance is provided for the following drives:

TS3100/TS3200 (3573) with LTO3 and LTO4 Fibre Channel drives.
TS3310 (3576) with LTO3 and LTO4 Fibre Channel drives.
TS3400 (3577) with 3592-E05 and 3592-E06 Fibre Channel drives.
TS3500 with LTO2, LTO3, LTO4, 3592-J1A Fibre Channel drives.
SAS attached tape devices and tape libraries.

Note: It is strongly recommended that you do not leave the above devices in a multipath configuration.

The following restrictions apply for these devices:

A different device description can be automatically varied on during each partition IPL for each multipath attached device.
It takes more time to process any Online at IPL requests for tape during partition IPL.
For these devices, there is a 9020 Product Activity Log entry with secondary code 00000050 created for every additional path to the device.
The system will not be able to recover from configuration changes and I/O path errors for these devices.

No multipath support

Multipath tape attachment is not supported for the following devices.

SCSI attached tape devices.
3494 tape library.

For more information about tape multipath support, see IBM Removable Media on IBM i

How to use tape multipath devices

For multipath attached tape library devices, there is a Media Library (MLB) device description that is created for each path to the tape library device that has a control path drive. The same tape device resource names are shown for each of the MLB device descriptions and they can be deallocated, allocated, or allocated unprotected as wanted with the WRKMLBSTS (Work with Media Library Status) command. The resource names that are shown in the WRKMLBSTS command do not always indicate the active path resource. Any varied on MLB device description with allocated resources can be used for commands.

For multipath attached stand-alone tape devices, a tape device description is created for only the preferred path to the tape device. If the preferred path is changed, a new device description is created for the resource that uses that path. The resource name that is associated with this device description might not be the resource name of the active path. The varied on device description can be used for commands.