HP StoreEver MSL2024, MSL4048, MSL8048, and MSL8096 Tape Libraries User and Service Guide (AK378-96059, December 2012)

Table Of Contents
If drive hosting the library control path fails, the library web interface may be used to take the
control path drive offline and the library control path identity (world wide names) and all settings,
(such as reservations and prevent/allow settings), will be moved over to the alternate master drive
automatically. When properly configured, the change is minimally disruptive to the host and does
not require any configuration changes on the host or in the backup application.
If no library commands are sent while the port is being reconfigured, the port change happens
with virtually no disruption to the SAN. Commands sent while the port is being reconfigured cannot
be processed and will fail. Applications that retry commands are able to use the library following
reconfiguration of the port. Applications that do not retry can be restarted remotely without making
any hardware configuration changes.
Figure 7 Control path port failover example configuration
2. Primary data path for drive 1 and active library control path1. Library drive 1 (embedded in library)
4. Primary data path for drive 2 and standby library control path3. Standby data path
6. Library drive 2 (embedded in library)5. Standby data path
7. Standby library control path (logical via control
link to drive)
Technology for drive-assisted failover
The drive-assisted failover features in HP LTO-5 and LTO-6 drives use Fibre Channel switched fabric
features to transfer a drive identity to a different port. The drive manages all of the SCSI
configurations so that the settings expected by the application are still present after the port change.
In a typical multi-path configuration the application must manage both paths and reconfigure the
drive any time the active path is changed.
Both data path port failover and control path port failover require at least one Fibre Channel switch
between the drive and the host to provide some of the features required for failover with minimal
host disruption.
Control path and data path failover 23