Novell LINUX ENTERPRISE SERVER 10 SP3 - ARCHITECTURE-SPECIFIC, Administration Manual

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Managing Multipath I/O for Devices 51
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Device Mapper Multipath detects every path for a multipathed device as a separate SCSI device.
The SCSI device names take the form
/dev/sd N
, where
N
is an autogenerated letter for the device,
beginning with a and issued sequentially as the devices are created, such as
/dev/sda
,
/dev/sdb
,
and so on. If the number of devices exceeds 26, the letters are duplicated so that the next device after
/dev/sdz
will be named
/dev/sdaa
,
/dev/sdab
, and so on.
If multiple paths are not automatically detected, you can configure them manually in the
/etc/
multipath.conf
file. The
multipath.conf
file does not exist until you create and configure it.
For information, see Section 5.4.5, “Creating and Configuring the /etc/multipath.conf File,” on
page 56 .
5.3.2 Multipath I/O Management Tools
The
multipath-tools
user-space package takes care of automatic path discovery and grouping. It
automatically tests the path periodically, 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.
Table 5-2
Tools in the multipath-tools Package
For a list of files included in this package, see the multipath-tools Package Description (http://
www.novell.com/products/linuxpackages/suselinux/multipath-tools.html) .
1 Ensure that the
multipath-tools
package is installed by entering the following at a terminal
console prompt:
rpm -q multipath-tools
If it is installed, the response repeats the package name and provides the version information,
such as:
multipath-tools-04.7-34.23
If it is not installed, the response reads:
package multipath-tools is not installed
Boot/Root device support Multipathing is supported for the root ( / ) device in SUSE Linux Enterprise
Server 10 and later. The host server must be connected to the currently
active controller and storage processor for the boot device. The
/boot
partition must be on a separate, non-multipathed partition. Otherwise, no
boot loader is written. For information, see
Section 5.8, “Configuring
Multipath I/O for the Root Device,” on page 67 .
Tool Description
multipath Scans the system for multipathed devices and assembles them.
multipathd Waits for maps events, then executes multipath .
devmap-name Provides a meaningful device name to
udev
for device maps (devmaps).
kpartx Maps linear devmaps to partitions on the multipathed device, which makes
it possible to create multipath monitoring for partitions on the device.
Features of Storage Arrays Description