Preparing the library
Advanced path failover is a licensed feature with Control Path Failover and Data Path Failover licensed
separately. Licenses for all failover solutions are also available as a high-availability bundle. Control Path
Failover provides path fault tolerance for the robot controller and Data Path Failover provides fault
tolerance for the tape drive data path. Each feature is licensed once for each tape library and then
enabled separately for every partition and tape drive. The settings may be different for different partitions
and drives depending on the user requirements.
When advanced path failover is enabled for either the control path or the data path, the library partition
and/or tape drives with advanced path failover enabled can only be used by hosts with the advanced path
failover driver installed. If the tape drive or tape library detects that advanced path failover is enabled and
a request to access the media or move media is received from a host that is not using an advanced path
failover driver, the drive or library will reject the command with an additional sense code of 82h/93h,
FAILOVER SESSION SEQUENCE ERROR. That error code should only be reported to an application if
the advanced path failover drivers are not installed on that host.
In a mixed environment where some hosts have advanced path failover drivers installed and some hosts
do not, the library should be partitioned so that one partition is accessed by hosts that are using
advanced path failover and the second partition is accessed by hosts that are not using advanced path
failover. In some cases a mix of host operating systems might be used with a single partition. For example
a Windows host might be running the library control agent and another operating system is performing
backups. In that configuration advanced control path failover could be enabled and the advanced path
failover driver installed on the library control host but the drives may be configured without path failover.
If a single ESL G3 library needs to serve both hosts that have advanced path failover drivers installed and
hosts without advanced path failover drivers, the ESL G3 library can be configured with pools of drives
where all of the hosts with advanced path failover drivers use one pool of drives and advanced data path
failover is enabled on those drives. At the same time, a second pool of drives in the same partition either
has basic data path failover enabled or no data path failover enabled. The second pool of drives is
accessed by the hosts that do not have advanced path failover drivers. Other libraries do not support
mixing basic and advanced path failover, so the drives connected to hosts without advanced path failover
drivers must be configured without path failover enabled.
For instructions on installing advanced path failover for your library, see:
• ESL G3:
Configuring failover for the ESL G3 Tape Libraries
• MSL3040 or MSL6480:
Configuring failover for the MSL3040 or MSL6480
on page 32
Preparing the host
Hosts used with advanced path failover must be configured with two different data paths and should be
configured with two different HBAs. For supported HBAs see the compatibility matrix on the Backup,
Recovery and Archive Solutions website:
NOTE:
Always verify that your HBA and HBA driver are supported with path failover. For example, the
Emulux HBA driver that is included in the Red Had distribution must be upgraded.
For the highest level of fault protection, connect two different HBAs in the host to two different SANs. This
configuration provides full fault tolerance from both an HBA failure and a SAN switch failure. If a single
HBA is used, an HBA failure might result in loss of connection.
The advanced path failover driver for Windows selects the first path it discovers. If you want the driver to
select a particular SAN path, configure the host so that the HBA for your preferred path is installed in the
position with the lowest numbered bus location. Refer to your server documentation for bus location
Preparing the library
19
