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/mpathais the name of a multipath device, the following command will mark
/dev/mapper/mpathaas a physical volume.
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.
If you attempt to create an LVM physical volume on a whole device on which you have configured partitions, the
pvcreatecommand 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 -dand the
fdiskcommands. If your system has block devices that are greater that 2Tb, you can use the
partedcommand 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
/etc/lvm/lvm.conffile 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
devicessection of the file.
filter = [ "r/block/", "r/disk/", "r/sd.*/", "a/.*/" ]