Multipath-Usage.txt - Red Hat CLUSTER SUITE - CONFIGURING AND MANAGING A CLUSTER 2006 Manual

Multipath-usage.txt

Enterprise Linux 4 Update 3
This appendix contains the
RPM and provides guidelines for using
dm-multipath
Cluster Suite for Red Hat Enterprise Linux 4 Update 3:
RHEL4 U3 Device Mapper Multipath Usage
Overview
------------
Device Mapper Multipath (DM-MP) allows nodes to route I/O over
multiple paths to a storage controller. A path refers to the
connection from an HBA port to a storage controller port. As paths
fail and new paths come up, DM-MP reroutes the I/O over the
available paths.
When there are multiple paths to a storage controller, each path
appears as a separate device.
those devices. For example, a node with two HBAs attached to a storage
controller with two ports via a single unzoned FC switch sees four
devices: /dev/sda, /dev/sdb, /dev/sdc, and /dev/sdd. DM-MP creates a
single device, /dev/mpath/mpath1 that reroutes I/O to those four
underlying devices.
DM-MP consists of the following components:
o dm-multipath kernel module -- This module reroutes I/O and fails
over paths and path groups.
o multipath command -- This command configures, lists, and removes
multipath devices. The command is run in rc.sysinit during startup,
and by udev, whenever a block device
o multipathd daemon -- This daemon monitors paths, checking to see
if faulty paths have been fixed. As paths come back up, multipathd
may also initiate path group switches to ensure that the optima
path group is being used. Also, it is possible to interactively
modify a multipath device.
o kpartx command -- This command creates Device Mapper devices for the
partitions on a device. It is necessary to use this command for DOS-
based partitions with DM-MP.
File for Red Hat
Multipath-usage.txt
DM-MP creates a new device on top of
Appendix C.
file. The file is included with the
dm-multipath
is added.
with Red Hat