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Multipath I/O Features of Storage Arrays
Table 7-1
Features of Storage Arrays
Active/passive controllers
Active/active controllers
Load balancing
Controller failover
Boot/Root device support
Device Mapper Multipath detects every path for a multipathed device as a separate SCSI device.
The SCSI device names take the form
beginning with a and issued sequentially as the devices are created, such as
and so on. If the number of devices exceeds 26, the letters are duplicated so that the next device after
will be named
/dev/sdz
If multiple paths are not automatically detected, you can configure them manually in the
file. The
multipath.conf
For information, see
Section 7.4.5, "Creating and Configuring the /etc/multipath.conf File," on
page
56.
7.3.2 Multipath I/O Management Tools
The
user-space package takes care of automatic path discovery and grouping. It
multipath-tools
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.
Description
One controller is active and serves all LUNs. The second controller acts as
a standby. The second controller also presents the LUNs to the multipath
component so that the operating system knows about redundant paths. If
the primary controller fails, the second controller takes over, and it serves
all LUNs.
In some arrays, the LUNs can be assigned to different controllers. A given
LUN is assigned to one controller to be its active controller. One controller
does the disk I/O for any given LUN at a time, and the second controller is
the standby for that LUN. The second controller also presents the paths,
but disk I/O is not possible. Servers that use that LUN are connected to
the LUN's assigned controller. If the primary controller for a set of LUNs
fails, the second controller takes over, and it serves all LUNs.
Both controllers share the load for all LUNs, and can process disk I/O for
any given LUN. If one controller fails, the second controller automatically
handles all traffic.
The Device Mapper Multipath driver automatically load balances traffic
across all active paths.
When the active controller fails over to the passive, or standby, controller,
the Device Mapper Multipath driver automatically activates the paths
between the host and the standby, making them the primary paths.
Multipathing is supported for the root (
Server 10 and later. The host server must be connected to the currently
active controller and storage processor for the boot device.
Multipathing is supported for the
Server 11 and later.
, where
/dev/sdN
,
, and so on.
/dev/sdaa
/dev/sdab
file does not exist until you create and configure it.
multipath.conf
/
) device in SUSE Linux Enterprise
device in SUSE Linux Enterprise
/boot
is an autogenerated letter for the device,
N
/dev/sda
Managing Multipath I/O for Devices
,
,
/dev/sdb
/etc/
51
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