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12.9. Troubleshooting duplicate physical volume warnings for multipathed LVM devices

When using LVM with multipathed storage, LVM commands that list a volume group or logical volume might display messages such as the following:

Copy to Clipboard Toggle word wrap 
Found duplicate PV GDjTZf7Y03GJHjteqOwrye2dcSCjdaUi: using /dev/dm-5 not /dev/sdd
Found duplicate PV GDjTZf7Y03GJHjteqOwrye2dcSCjdaUi: using /dev/emcpowerb not /dev/sde
Found duplicate PV GDjTZf7Y03GJHjteqOwrye2dcSCjdaUi: using /dev/sddlmab not /dev/sdf

You can troubleshoot these warnings to understand why LVM displays them, or to hide the warnings.

12.9.1. Root cause of duplicate PV warnings

When a multipath software such as Device Mapper Multipath (DM Multipath), EMC PowerPath, or Hitachi Dynamic Link Manager (HDLM) manages storage devices on the system, each path to a particular logical unit (LUN) is registered as a different SCSI device.

The multipath software then creates a new device that maps to those individual paths. Because each LUN has multiple device nodes in the /dev directory that point to the same underlying data, all the device nodes contain the same LVM metadata.

Tableau 12.1. Example device mappings in different multipath software
Multipath softwareSCSI paths to a LUNMultipath device mapping to paths

DM Multipath

/dev/sdb and /dev/sdc

/dev/mapper/mpath1 or /dev/mapper/mpatha

EMC PowerPath

/dev/emcpowera

HDLM

/dev/sddlmab

As a result of the multiple device nodes, LVM tools find the same metadata multiple times and report them as duplicates.

12.9.2. Cases of duplicate PV warnings

LVM displays the duplicate PV warnings in either of the following cases:

Single paths to the same device

The two devices displayed in the output are both single paths to the same device.

The following example shows a duplicate PV warning in which the duplicate devices are both single paths to the same device.

Copy to Clipboard Toggle word wrap 
Found duplicate PV GDjTZf7Y03GJHjteqOwrye2dcSCjdaUi: using /dev/sdd not /dev/sdf

If you list the current DM Multipath topology using the multipath -ll command, you can find both /dev/sdd and /dev/sdf under the same multipath map.

These duplicate messages are only warnings and do not mean that the LVM operation has failed. Rather, they are alerting you that LVM uses only one of the devices as a physical volume and ignores the others.

If the messages indicate that LVM chooses the incorrect device or if the warnings are disruptive to users, you can apply a filter. The filter configures LVM to search only the necessary devices for physical volumes, and to leave out any underlying paths to multipath devices. As a result, the warnings no longer appear.

Multipath maps

The two devices displayed in the output are both multipath maps.

The following examples show a duplicate PV warning for two devices that are both multipath maps. The duplicate physical volumes are located on two different devices rather than on two different paths to the same device.

Copy to Clipboard Toggle word wrap 
Found duplicate PV GDjTZf7Y03GJHjteqOwrye2dcSCjdaUi: using /dev/mapper/mpatha not /dev/mapper/mpathc

Found duplicate PV GDjTZf7Y03GJHjteqOwrye2dcSCjdaUi: using /dev/emcpowera not /dev/emcpowerh

This situation is more serious than duplicate warnings for devices that are both single paths to the same device. These warnings often mean that the machine is accessing devices that it should not access: for example, LUN clones or mirrors.

Unless you clearly know which devices you should remove from the machine, this situation might be unrecoverable. Red Hat recommends that you contact Red Hat Technical Support to address this issue.

12.9.3. Example LVM device filters that prevent duplicate PV warnings

The following examples show LVM device filters that avoid the duplicate physical volume warnings that are caused by multiple storage paths to a single logical unit (LUN).

You can configure the filter for logical volume manager (LVM) to check metadata for all devices. Metadata includes local hard disk drive with the root volume group on it and any multipath devices. By rejecting the underlying paths to a multipath device (such as /dev/sdb, /dev/sdd), you can avoid these duplicate PV warnings, because LVM finds each unique metadata area once on the multipath device itself.

  • To accept the second partition on the first hard disk drive and any device mapper (DM) Multipath devices and reject everything else, enter:

    Copy to Clipboard Toggle word wrap 
    filter = [ "a|/dev/sda2$|", "a|/dev/mapper/mpath.*|", "r|.*|" ]

  • To accept all HP SmartArray controllers and any EMC PowerPath devices, enter:

    Copy to Clipboard Toggle word wrap 
    filter = [ "a|/dev/cciss/.*|", "a|/dev/emcpower.*|", "r|.*|" ]

  • To accept any partitions on the first IDE drive and any multipath devices, enter:

    Copy to Clipboard Toggle word wrap 
    filter = [ "a|/dev/hda.*|", "a|/dev/mapper/mpath.*|", "r|.*|" ]

12.9.4. Ressources supplémentaires

Ressources supplémentaires

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