Novell LINUX ENTERPRISE SERVER 11 - STORAGE ADMINISTRATION GUIDE 2-23-2010, Руководство администратора, Страница: 62 / 140

62 SLES 11: Storage Administration Guide
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“Configuring for Single Path Failover” on page 66
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“Grouping I/O Paths for Round-Robin Load Balancing” on page 66
Understanding Priority Groups and Attributes
A priority group is a collection of paths that go to the same physical LUN. By default, I/O is
distributed in a round-robin fashion across all paths in the group. The
multipath
command
automatically creates priority groups for each LUN in the SAN based on the path_grouping_policy
setting for that SAN. The
multipath
command multiplies the number of paths in a group by the
group’s priority to determine which group is the primary. The group with the highest calculated
value is the primary. When all paths in the primary group are failed, the priority group with the next
highest value becomes active.
A path priority is an integer value assigned to a path. The higher the value, the higher is the priority.
An external program is used to assign priorities for each path. For a given device, the paths with the
same priorities belong to the same priority group.
Table 7-5
Multipath Attributes
Multipath Attribute Description Values
user_friendly_names Specifies whether to use IDs
or to use the
/var/lib/
multipath/bindings
file
to assign a persistent and
unique alias to the multipath
devices in the form of
/dev/
mapper/mpathN
.
yes: Autogenerate user-friendly names as
aliases for the multipath devices instead of the
actual ID.
no: Default. Use the WWIDs shown in the /
dev/disk/by-id/
location.
blacklist Specifies the list of device
names to ignore as non-
multipathed devices, such as
cciss, fd, hd, md, dm, sr, scd,
st, ram, raw, loop. For an example, see “Blacklisting Non-
Multipathed Devices in /etc/multipath.conf” on
page 58
.
blacklist_exceptions Specifies the list of device
names to treat as multipath
devices even if they are
included in the blacklist. For an example, see the
/usr/share/doc/
packages/multipath-tools/
multipath.conf.annotated
file.
getuid The default program and
arguments to call to obtain a
unique path identifier. Should
be specified with an absolute
path.
/sbin/scsi_id -g -u -s
This is the default location and arguments.
Example:
getuid "/sbin/scsi_id -g -u -d /dev/
%n"