About Data Path Failover

Data Path Failover is one of the features of the Storage Networking license and applies to LTO-5 and higher Fibre Channel tape drives only. The drive type required depends on the type of Data Path Failover you want to use:

• Standard (HP and/or IBM drives) - Provides no redundant path to the partition.
• Basic Path Failover (HP LTO-5 and higher drives) - Provides a single redundant path to the partition.
• Multi-Path (HP and/or IBM LTO-5 and higher dual-port FC drives) - Provides multiple redundant paths to the partition.
• Advanced Path Failover (IBM LTO-6 and higher dual-port FC drives) - Provides multiple redundant paths to the partition while shielding applications from handling multiple connection paths to a drive and/or library partition

HP LTO-5 and higher Fibre Channel tape drives have two Fibre Channel ports. If you enable data path failover on the tape drive, one port will be used as the “active port” for data transmission, and the other port will stand by to be used if the active port fails. If the tape drive loses its Fibre Channel link with the active port, it will automatically “fail over” and use the standby port to continue drive operations. The library issues a RAS ticket when automatic failover occurs. In addition, the library monitors the standby port and issues a RAS ticket if the standby port does not report a good Fibre Channel link status.

The library uses Port 1 for data path transmission unless a failover occurs. Once failover occurs, the library uses Port 2 until failover occurs again or the library is rebooted. Similarly, if a tape drive configured for data path failover is the control path for a partition, the host uses Port 1 for media changer commands unless a failover occurs. Once failover occurs, the host uses Port 2 until failover occurs again or the library is rebooted.

NOTE: Performing a drive reset operation is another way to make Port 1 the active port again, unless the reason Port 2 is active is due to a forced failover (see Forcing Data Path Failover). If you forced a failover to Port 2 and then reset the tape drive, the library and host will continue to use Port 2 until failover occurs again or the library is rebooted.

A tape drive can be configured for both data path failover and control path failover. If both are configured, the control path will not fail over to another tape drive unless both ports on the control path tape drive fail.

If desired, you can manually switch the active Fibre Channel port by forcing data path failover.

NOTE: If you are NOT using data path failover, the library only uses Port 1 for data path transmission. Port 2 is only recognized by the library when data path failover is enabled on the tape drive.

Enabling Data Path Failover

1. Connect both tape drive Fibre Channel ports (Port 1 and Port 2) to a host or switch (NOT to a Fibre Channel I/O blade).
2. Make sure you have a Storage Networking license sufficient to cover the tape drive(s) on which you want to configure data path failover.
3. Make sure the tape drives are LTO-5 and higher Fibre Channel drives running the latest version of firmware qualified for the library. See the library release notes for the appropriate firmware.
4. From the library Setup menu, click Drive Settings.
   
   The Setup - Drive Settings page displays.
5. For each tape drive on which you want to enable data path failover, do the following:
   
   1. Change the Requested Topology setting to Point to Point.
   2. Select the type of Data Path from the list.
6. Click Apply.

See also:

• About Tape Drive Operations
• Setting Tape Drive Parameters
• Forcing Data Path Failover
• Applying a License Key