Chapter 2. Multipath Devices
6
a cluster. For information on the
multipaths
section of the multipath configuration file, see see
Section 4.4, “Multipaths Device Configuration Attributes”
.
• If you want the system-defined user-friendly names to be consistent across all nodes in the cluster,
set up all of the multipath devices on one machine. Then copy the
/var/lib/multipath/
bindings
file from that machine to all the other machines in the cluster.
2.3. Multipath Device Attributes
In addition to the
user_friendly_names
and
alias
options, a multipath device has numerous
attributes. You can modify these attributes for a specific multipath device by creating an entry for
that device in the
multipaths
section of the multipath configuration file. For information on the
multipaths
section of the multipath configuration file, see see
Section 4.4, “Multipaths Device
Configuration Attributes”
.
2.4. Multipath Devices in Logical Volumes
After creating multipath devices, you can use the multipath device names just as you would use a
physical device name when creating an LVM physical volume. For example, if
/dev/mapper/mpath0
is the name of a multipath device, the following command will mark
/dev/mapper/mpath0
as a
physical volume.
pvcreate /dev/mapper/mpath0
You can use the resulting LVM physical device when you create an LVM volume group just as you
would use any other LVM physical device.
Note
If you attempt to create an LVM physical volume on a whole device on which you have
configured partitions, the
pvcreate
command will fail. Note that the Anaconda and
Kickstart installation programs create empty partition tables if you do not specify otherwise
for every block device. If you wish to use the whole device rather than a partition, you
must remove the existing partitions from the device. You can remove existing partitions
with the
kpartx -d
and the
fdisk
commands. If your system has block devices that are
greater that 2Tb, you can use the
parted
command to remove partitions.
When you create an LVM logical volume that uses active/passive multipath arrays as the underlying
physical devices, you should include filters in the
lvm.conf
to exclude the disks that underlie the
multipath devices. This is because if the array automatically changes the active path to the passive
path when it receives I/O, multipath will failover and failback whenever LVM scans the passive path if
these devices are not filtered. For active/passive arrays that require a command to make the passive
path active, LVM prints a warning message when this occurs.
To filter all SCSI devices in the LVM configuration file (
lvm.conf
), include the following filter in the
devices
section of the file.
filter = [ "r/disk/", "r/sd.*/", "a/.*/" ]
