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2.2. Multipath devices in logical volumes

Multipath devices integrate seamlessly with LVM, allowing you to create physical volumes, volume groups, and logical volumes by using multipath device names instead of individual disk paths.

After creating multipath devices, you can use the multipath device names as you would use a physical device name when creating an Logical volume manager (LVM) physical volume. For example, if /dev/mapper/mpatha is the name of a multipath device, the pvcreate /dev/mapper/mpatha command marks /dev/mapper/mpatha as 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.

To filter all the sd devices in the /etc/lvm/lvm.conf file, add the filter = [ "r/block/", "r/disk/", "r/sd./", "a/./" ] filter in the devices section of the file. For more information see the lvm.conf man page on your system.

注意

If you attempt to create an LVM physical volume on a whole device on which you have configured partitions, the pvcreate command fails. The Anaconda and Kickstart installation programs create empty partition tables if you do not specify otherwise for every block device. If you want to use the whole device instead of creating a partition, remove the existing partitions from the device. You can remove existing partitions with the kpartx -d device command and the fdisk utility. If your system has block devices that are greater than 2Tb, use the parted utility to remove partitions.

When you create an LVM logical volume that uses active/passive multipath arrays as the underlying physical devices, you can optionally include filters in the /etc/lvm/lvm.conf file to exclude the disks that underline 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.

The kernel changes the active/passive state by automatically detecting the correct hardware handler to use. For active/passive paths that require intervention to change their state, multipath automatically uses this hardware handler to do so as necessary. If the kernel does not automatically detect the correct hardware handler to use, you can configure which hardware handler to use in the multipath.conf file with the "hardware_handler" option. For active/passive arrays that require a command to make the passive path active, LVM prints a warning message when this occurs.

Depending on your configuration, LVM may print any of the following messages:

  • LUN not ready: 

    end_request: I/O error, dev sdc, sector 0
sd 0:0:0:3: Device not ready: <6>: Current: sense key: Not Ready
    Add. Sense: Logical unit not ready, manual intervention required

  • Read failed: 

    /dev/sde: read failed after 0 of 4096 at 0: Input/output error

The following are the reasons for the mentioned errors:

  • Multipath is not set up on storage devices that are providing active/passive paths to a machine.
  • Paths are accessed directly, instead of through the multipath device.
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