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

reliability enhancements to the MSL2024, MSL4048, MSL8048, and MSL8096 Tape Libraries
with LTO-5 and LTO-6 Fibre Channel tape drives.
• Data path port failover where a standby path is configured for the data path to the tape drive
and activated following link failures.
• Library control path port failover where a second drive is configured to host a standby library
control path that can be activated following link failures.
Failover functionality in the HP LTO-5 tape drives and HP LTO tape libraries transfers the active
path and all settings to the standby path following failures.
HP LTO-5 and LTO-6 data path port failover overview
Data path port failover (see “Data path port failover example configuration” (page 22)) may be
configured on each dual-port Fibre Channel tape drive. When data path port failover is configured
one link is active and is the primary data path. The second link is a standby data path. The drive
will verify that the second link is able to receive a Fibre Channel signal and complete speed
negotiation but the drive will not log into the SAN using the standby link.
The drive monitors the links for errors and following detection of a fault, transfers the fabric identity
(world wide names) and all settings (mode parameters, encryption settings, etc.) over to the standby
link then activates that link. 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 drive commands are outstanding when a failure is detected, then the port change happens
with virtually no disruption to the SAN. If a command is outstanding on the link when a failure is
detected the drive is not able to recover the command so that command will fail but the application
will be able to continue to use the drive on the new path. Many applications are able to recover
from a single command failure as long as the communication path to the drive is not lost.
Figure 6 Data path port failover example configuration
2. Standby data path1. Primary data path
4. Standby data path3. Primary data path
6. LTO-5 FC tape drive5. LTO-5 FC tape drive
HP LTO-5 and LTO-6 control path failover overview
Library control path port failover (see “Control path port failover example configuration” (page 23))
may be configured with one drive hosting the path to the library controller and a second drive
configured as an alternate standby path to the library controller. The library connections will share
physical links with the drives but the library will have its own identity on the SAN. If data path port
failover is also configured, the library control path will follow the data path on link failures.
22 Features and overview