Benefits Of Multipathing; Guidelines For Multipathing; Multipath Management Tools; Section 5.2, "Multipath Management Tools - Novell LINUX ENTERPRISE SERVER 10 - STORAGE ADMINISTRATION GUIDE 7-2007 Administration Manual

5.1.2 Benefits of Multipathing

Linux multipathing provides connection fault tolerance and can optionally provide load balancing
across the available connections. When multipathing is configured and running, it automatically
isolates and identifies device connection failures, and reroutes I/O to alternate connections.
Typical connection problems involve faulty adapters, cables, or controllers. When you configure
multipath I/O for a device, the multipath driver monitors the active connection between devices.
When it detects I/O errors, the multipath driver fails over to a designated secondary path. When the
primary path becomes healthy again, control is automatically returned to the primary connection.

5.1.3 Guidelines for Multipathing

Use the guidelines in this section when planning your multipath I/O solution:

5.2 Multipath Management Tools

The multipath I/O support in SUSE Linux Enterprise Server is based on the Device Mapper
Multipath I/O module of the Linux kernel and the multipath-tools userspace package. Use
mdadm to view the status of multipathed devices.
44 SLES 10 Storage Administration Guide
Multipathing is managed at the device level.
Multiple physical paths must exist between host bus adapters in the server and host bus
controllers for the block storage device.
Device partitioning (disk carving) and hardware RAID configuration should be completed
prior to configuring multipathing. If you change the partitioning in the running system, Device
Mapper Multipath I/O (DM-MPIO) does not automatically detect and reflect these changes. It
must be reinitialized, which usually requires a reboot.
When you plan to create software RAID devices, multipathing should be configured for the
devices you plan to use prior to creating the software RAID devices because multipathing runs
underneath the RAID.
When you plan to create a Distributed Replicated Block Device (DRBD), multipathing should
be configured for the devices prior to configuring the DRBD because multipathing runs
underneath the DRBD.
The storage subsystem you use on the multipathed device must support multipathing. Most
storage subsystems should work; however, they might require an appropriate entry in the
DEVICE variable in the /etc/multipath.conf file.
Consult the vendor's hardware documentation to determine what settings are required.
When configuring devices for multipathing, use the device names in the /dev/disk/by-id
directory instead of the default device names (such as /dev/sd*), because the /dev/disk/
by-id names persist over reboots.
For more information, see
Device Mapper Multipath I/O supports partitions (with limitations) and LVM2. Software RAID
is also supported, but automatic discovery is not available.
Section 5.2.1, "Device Mapper Multipath I/O Module," on page 45
Section 5.2.2, "Multipath I/O Management Tools," on page 45
Section 5.2.3, "Using mdadm for Multipathed Devices," on page 46
Chapter 3, "Using UUIDs to Mount Devices," on page 31.