Multipath Management Tools; Device Mapper Multipath Module - Novell LINUX ENTERPRISE SERVER 11 - STORAGE ADMINISTRATION GUIDE 2-23-2010 Administration Manual

7.3 Multipath Management Tools

The multipathing support in SUSE Linux Enterprise Server 10 and later is based on the Device
Mapper Multipath module of the Linux 2.6 kernel and the
You can use
Section 7.3.1, "Device Mapper Multipath Module," on page 50
Section 7.3.2, "Multipath I/O Management Tools," on page 51
Section 7.3.3, "Using mdadm for Multipathed Devices," on page 52
Section 7.3.4, "The Linux multipath(8) Command," on page 53

7.3.1 Device Mapper Multipath Module

The Device Mapper Multipath (DM-MP) module provides the multipathing capability for Linux.
DM-MP is the preferred solution for multipathing on SUSE Linux Enterprise Server 11. It is the
only multipathing option shipped with the product that is completely supported by Novell
SUSE.
DM-MP features automatic configuration of the multipathing subsystem for a large variety of
setups. Configurations of up to 8 paths to each device are supported. Configurations are supported
for active/passive (one path active, others passive) or active/active (all paths active with round-robin
load balancing).
The DM-MP framework is extensible in two ways:
Using specific hardware handlers. For information, see
Hardware Handlers" on page
Using more sophisticated load-balancing algorithms than round-robin
The user-space component of DM-MP takes care of automatic path discovery and grouping, as well
as automated path retesting, so that a previously failed path is automatically reinstated when it
becomes healthy again. This minimizes the need for administrator attention in a production
environment.
DM-MP protects against failures in the paths to the device, and not failures in the device itself. If
one of the active paths is lost (for example, a network adapter breaks or a fiber-optic cable is
removed), I/O is redirected to the remaining paths. If the configuration is active/passive, then the
path fails over to one of the passive paths. If you are using the round-robin load-balancing
configuration, the traffic is balanced across the remaining healthy paths. If all active paths fail,
inactive secondary paths must be waked up, so failover occurs with a delay of approximately 30
seconds.
If a disk array has more than one storage processor, make sure that the SAN switch has a connection
to the storage processor that owns the LUNs you want to access. On most disk arrays, all LUNs
belong to both storage processors, so both connections are active.
NOTE: On some disk arrays, the storage array manages the traffic through storage processors so
that it presents only one storage processor at a time. One processor is active and the other one is
passive until there is a failure. If you are connected to the wrong storage processor (the one with the
passive path) you might not see the expected LUNs, or you might see the LUNs but get errors when
trying to access them.
50 SLES 11: Storage Administration Guide
to view the status of multipathed devices.
mdadm
49.
userspace package.
multipath-tools
"Storage Arrays that Require Specific
®
and