When you load the ATDD device driver with the alternate_pathingparameter set to ON, by default, all the available paths for a physical device are enabled.
If it is necessary to disable a path and not perform path fail over (for example due to maintenance), run commands to disable and then later enable the primary and alternate paths.
The commands to enable and disable primary and alternate paths are tape diagnostic and utility functions.
Note: See Chapter 10, “IBM Tape Diagnostic Tool (ITDT),” on page 259 or “HP-UX System - Tape Utility Program (tapeutil)” on page 375
Data Path Failover and Load Balancing Support for Tape Drives
The HP-UX device driver path failover support configures multiple physical paths to the same device within the device driver and provides two basic functions:
1. Automatic failover to an alternate physical path when a permanent error occurs on one path.
2. Dynamic load balancing for devices using multiple Host Bus Adapters (HBA). On HP-UX 11i v3, HP-UX system always pickups a best path for ATDD to open; ATDD doesn't perform a dynamic load balancing in open.
Notes:
1. Data Path Failover is not supported when using block sizes greater than 256K, except in HP-UX 11i v3.
2. It is required that applications must open the primary path for Data Path Failover (not in HP-UX 11i v3).
3. Data Path Failover is supported for 3592 tape drives on HP-UX 11.0, 11i v1, v2 and v3, and for Ultrium-3 and Ultrium-4 drives on HP-UX 11i v1, v2 and v3.
Configuring and Unconfiguring Path Failover Support
Path failover support is turned on automatically when the device driver is installed. However, you need to provide the data path failover feature key and reclaim the devices using the atdd_claim script. The feature key is a string with 16 characters and numbers.
To enable the failover support in the IBMtape device driver software, perform the following steps after installing the driver:
1. Edit the following line in your /sbin/init.d/atddfile: DPF_KEYS="1234567890123456; 0987654321123456 "
Notes:
a. ″1234567890123456″is an example of a data path failover feature key. If you have multiple 3584 libraries and multiple data path failover feature keys, input your keys as follows:DPF_KEYS="key1; key2; ..."
b. A DPF key is required for Ultrium-3 tape drives only. No DPF key needs to be added into the/sbin/init.d/atddfile if you are running the most recent drive code.
2. Save the file, then run the following command in HP-UX 11.0, 11i v1 and v2: # /opt/atdd/bin/atdd_claim
3. In HP-UX 11.0, 11i v1 and v2, you can check whether the driver has recognized multiple data paths for your drives by running:
#ioscan -funC tape
If you see a".altpath"next to one of the special files, then you have successfully enabled control path failover feature for your library.
In HP-UX 11i v3, use the # ioscan -m dsfcommand and the option 53 of “Display Path” in tapeutil to verify that the multiple path is configured by the system and ATDD.
Note: See Chapter 10, “IBM Tape Diagnostic Tool (ITDT),” on page 259 or “HP-UX System - Tape Utility Program (tapeutil)” on page 375
After path failover support is enabled, it remains set until atdd_claimorkctuneis run with thealternate_pathingdriver parameter set to OFF. The path failover setting is retained even if the system is rebooted. If you want to turn off the data path failover feature in the ATDD driver, perform the following steps:
In HP-UX 11.0, 11i v1 and v2:
1. Clear thealternate_pathing parameter. (You can ignore the message about rebooting the system.)# /opt/atdd/bin/atdd_failover -a 0
2. Reconfigure DPF for the devices: # /opt/atdd/bin/atdd_claim In HP-UX 11i v3:
Run kctune to disable the kernel tunable of atdd_alternate_pathing. ATDD handles the DPF in the next open.
# kctune atdd_alternate_pathing=0
* The automatic 'backup' configuration has been updated. * The requested changes have been applied to the currently
running configuration.
Tunable Value Expression Changes
atdd_alternate_pathing (before) 1 1 Immed
(now) 0 0
If you want to turn the data path failover feature back on in the ATDD driver, perform the following steps:
In HP-UX 11.0, 11i v1 and v2:
1. Set thealternate_pathingparameter. (You can ignore the message about rebooting the system.)
# /opt/atdd/bin/atdd_failover -a 1
2. Reconfigure DPF for the devices: # /opt/atdd/bin/atdd_claim In HP-UX 11i v3:
Run kctune to enable the kernel tunable of atdd_alternate_pathing. ATDD handles the DPF in the next open.
# kctune atdd_alternate_pathing=1
* The automatic 'backup' configuration has been updated. * The requested changes have been applied to the currently
running configuration.
Tunable Value Expression Changes
atdd_alternate_pathing (before) 0 0 Immed
(now) 1 1
Primary and Alternate Paths
When ATDD is loaded into the kernel, the first logical device that it sees in the system is the primary path for that medium changer. The other logical paths that ATDD attached for the same tape drive are configured as alternate paths. The device driver supports up to 16 physical paths for a single device. In HP-UX 11i v3, the HP-UX system always pickups a best path for ATDD to open so the primary path is dynamically assigned from the system. ATDD does not provide any .atlpath special file.
The primary and alternate path information can be obtained by issuing the following command except in HP-UX 11i v3:
# ioscan -funC tape
The following is an example of the output for this command: /home/root# ioscan -funC tape
Class I H/W Path Driver S/W State H/W Type Description
===============================================================================
tape 0 0/1/0/0.101.22.255.1.1.1 atdd CLAIMED DEVICE IBM ULT3580-TD3 /dev/rmt/0m
tape 1 0/1/0/0.101.22.255.1.2.1 atdd CLAIMED DEVICE IBM ULT3580-TD3 /dev/rmt/1m.altpath
Querying Primary and Alternate Path Configuration
You can display the primary and alternate path configuration for all devices by runningioscan, as explained in section “Primary and Alternate Paths” on page 84.
Note: Display the primary and alternate path configuration for any device using tape diagnostic and utility functions, refer to Chapter 10, “IBM Tape Diagnostic Tool (ITDT),” on page 259 or “HP-UX System - Tape Utility Program (tapeutil)” on page 375.
Disable and Enable Primary and Alternate Paths
If it is necessary to disable a path and not perform path fail over (for example due to maintenance), run commands to disable and then later enable the primary and alternate paths.
The commands to enable and disable primary and alternate paths are tape diagnostic and utility functions.
Note: See Chapter 10, “IBM Tape Diagnostic Tool (ITDT),” on page 259 or “HP-UX System - Tape Utility Program (tapeutil)” on page 375
Problem Determination
A set of tools is provided with the device driver to determine if the device driver and the tape device are functioning correctly.
Error Logging
Read the system log file (typically /var/adm/syslog/syslog.log) and the ATDD log file (/var/adm/atdd/atdd_d.log) if you are having problems. The ATDD logs messages to this file which provide information regarding the problem.
Reservation Conflict Logging
When the device driver receives a reservation conflict during open or after the device has been opened it will log a reservation conflict in the HP-UX system log of /var/adm/syslog/syslog.log. Prior to logging the error the device driver will issue a Persistent Reserve In command to determine if a SCSI Persistent Reservation is active on the reserving host to get the reserving host initiator WWPN (World Wide Port Name) and reserve key. If successful, the device driver will log this
information in the detail data below. After initially logging the reserving host WWPN, subsequent reservation conflicts from the same reserving host WWPN and reservation key will not be logged to prevent multiple entries in the system log until either the reserving host WWPN or reservation key is different than the one initially logged or the device driver has reserved the device and then another reservation conflict occurs.
1. The information is logged when the drive is reserved with a Persistent Reservation.
atdd: device=rtape41 Reserved. Reserving host key DF25382049E627E6 WWPN 21:00:00:E0:8B:11:8B:B1
2. The information is logged when the drive is reserved with a SCSI-2 Reserve. atdd: device=rtape41 Reserved. Device reserved with legacy reserve.