Database Reference
In-Depth Information
Using default value
2048
Last sector, +sectors or +size{K,M,G} (2048-4196351, default 4196351):
Using default value 4196351
Command (m for help):
w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
This example created a primary partition on a SCSI device. With such a device partitioned, you can start
configuring the multipath software.
Configuring dm-multipath
The principle behind any multipathing software is simple. Without the abstraction layer, the operating “sees” each
block device once via each path. That means a LUN can be
/dev/sdb
and additionally
/dev/sdk
-but still be the same
physical device, just using two different paths to the storage. Without a multipath driver the operating system could
not easily assess that two devices are logically the same. Thanks to the driver however this becomes possible. Instead
of using the native devices a new device is introduced to which the application (read: Oracle) sends I/O requests.
The pseudo device is created in a number of different places:
•
In the /dev directory such as /dev/dm-35
•
Again in the /dev directory, but with /dev/mpath
n
or a WWID
•
In the /dev/mapper directory with a user defined alias
In the case of the
dm-multipath
package, the mapping between block device and pseudo-device is performed in
the main configuration file:
/etc/multipath.conf
. An important aspect is to only use the pseudo-device. Otherwise
there would be no protection from path failures or no performance gains!
The installation of Oracle Linux comes with the multipath package installed as part of the standard installation.
If the package is not yet available, you should install the package
device-mapper-multipath.x86_64
including all its
dependencies. When installed, you need to ensure that the multipath process is started at every system boot-this is
done via the
chkconfig
application as shown here:
# chkconfig --level 35 multipathd on
# chkconfig --list | grep -i multipath
multipathd 0:off 1:off 2:off 3:on 4:off 5:on 6:off
Unlike Oracle Linux 5, there is no example content in
/etc/multipath.conf
-the file does not exist. A number
of example configurations are available in the documentation directory. That directory is named as follows,
but replacing
version
with your own version number:
/usr/share/doc/device-mapper-multipath-version.
The quickest way to starting with a basic failover scenario is to use the recommendation from the online
documentation by using the mpathconf utility as shown here:
# mpathconf --enable --with_multipathd y
# echo $?
0
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