HP StorageWorks Device Mapper Multipath Enablement Kit for HP StorageWorks Disk Arrays installation and reference guide (AA-RW8RE-TE, June 2009)

Paths are grouped based on the path grouping policy. In the previous example, for LUN mpath85,
the paths are grouped with the policy as multibus and the devices sdb, sda, sdf, sdi, sdg, sdh,
sdac, and sdae belong to the same path group.
For the LUN mpath86, the grouping is done with the policy as group_by_prio.
The devices sdc, sdk, sdj, and sdt belong to one path group, and the devices sdr, sdu, sdv,
and sdw belong to a different path group. This path grouping is based on one path group per path
priority value. Path priority value is determined by ALUA state of the path.
The I/O always happens in the path group which is active. If all paths in the active group fails, the
failover occurs to the other path group that is enabled on changing that path group to active. When
the paths are up again and the failback parameter is set as immediate, the failback occurs to the
earlier group and I/O occurs through the earlier group.
Example 2. Failover and Failback
If all the paths in a path group where I/Os are active fails, then I/Os are failed over to other path
groups. I/Os are failed back as soon as the failed paths become alive.
The state of the path is given as [active] [ready] if the path is up, and ready for I/O. If the path is
down, this state is shown as [failed] [faulty]. The path states are updated periodically based on the
polling interval set in the /etc/multipath.conf file. The path states are updated by the
multipathd daemon.
Table 3 lists the basic operations supported by the multipath CLI utility provided with DM Multipath.
Table 3 Basic operations of DM Multipath
DescriptionCommand
Deletes all DM Multipath devices.
# multipath –F
Displays potential paths, but does not create any device.
# multipath –d
Creates DM Multipath devices.
# multipath
Displays the list of device status.
Displays the detailed list of device status.
# multipath -l
# multipath -ll
Configures multipath map information
#multipath -v0
Clustering Solutions with DM Multipath
DM Multipath supports the following clustering solutions:
• HP Serviceguard for Linux version 11.18 or later
• SteelEye Lifekeeper for Linux version 6.1.4 or later
Configuring HP Service Guard with DM Multipath devices
DM Multipath devices can be used for data storage under Serviceguard protection. To configure DM
Multipath devices under Serviceguard, complete the following steps:
1. Configure the SAN such that each host has multiple paths to the array. Present the LUN’s to all
the hosts.
2. See Configure DM Multipath for configuring the LUN’s for DM Multipath
Using DM Multipath20