Question: LVM commands (such as vgs, lvchange, etc) display messages like this when trying to list VG or LV:
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
How can I get rid of duplicate PV messages display by LVM commands?
With a default configuration, LVM commands will scan for devices in /dev, and check every resulting device for LVM metadata. This is caused by the default filter in /etc/lvm/lvm.conf:
# cat /etc/lvm/lvm.conf filter = [ "a/.*/" ]
When using device-mapper-multipath or other multipath software such as EMC PowerPath or Hitachi Dynamic Link Manager (HDLM), each path to a particular logical unit number (LUN) is registered as a different SCSI device, such as /dev/sdb, /dev/sdc, and so on. The multipath software will then create a new device that maps to those individual paths, such as /dev/mapper/mpath1 or /dev/mapper/mpatha for device-mapper-multipath, /dev/emcpowera for EMC PowerPath, or /dev/sddlmab for Hitachi HDLM. Since each LUN has multiple device nodes in /dev that point to the same underlying data, they all contain the same LVM metadata and thus LVM commands will find the same metadata multiple times and report them as duplicates.
These messages are only warnings and do not mean the LVM operation has failed. Rather, they are alerting the user that only one of the devices has been used as a physical volume and the others are being ignored. To avoid this situation, a filter should be applied to only search the necessary devices for physical volumes, and to leave out any underlying paths to multipath devices.
Case 1: The two devices displayed in the output are both single paths to the same device
Example:
Found duplicate PV GDjTZf7Y03GJHjteqOwrye2dcSCjdaUi: using **/dev/sdd** not **/dev/sdf**
Here, sdd and sdf can both be found under the same multipath map, in the “# multipath -ll” output.
In this case, a filter can be configured in /etc/lvm/lvm.conf to restrict the devices that LVM will search for metadata. The filter is a list of patterns that will be applied to each device found by a scan of /dev (or the directory specified by the dir keyword in lvm.conf). Patterns are regular expressions delimited by any character and preceded by a (for accept) or r (for reject). The list is traversed in order, and the first regex that matches a device determines if the device will be accepted or rejected (ignored). Devices that don’t match any patterns are accepted.
This filter should include all devices that need to be checked for LVM metadata, such as the local hard 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, etc) you can avoid these duplicate PV warnings, since each unique metadata area will only be found once on the multipath device itself.
Example filters that will avoid duplicate PV warnings due to multiple storage paths being available:
To accept the second partition on the first hard drive (/dev/sda) and any device-mapper-multipath devices, while rejecting everything else:
filter = [ "a|/dev/sda2$|", "a|/dev/mapper/mpath.*|", "r|.*|" ]
To accept all HP SmartArray controllers and any EMC PowerPath devices:
filter = [ "a|/dev/cciss/.*|", "a|/dev/emcpower.*|", "r|.*|" ]
To accept any partitions on the first IDE drive and any multipath devices:
filter = [ "a|/dev/hda.*|", "a|/dev/mapper/mpath.*|", "r|.*|" ]
Once a filter has been configured and lvm.conf saved, check the output of these commands to ensure that no physical volumes or volume groups are missing:
# pvscan # vgscan
The filter can also be tested on the fly, without having to modify /etc/lvm/lvm.conf adding the “–config” argument to the LVM command. For example:
# lvs --config 'devices{ filter = [ "a|/dev/emcpower.*|", "r|.*|" ] }'
Once the desired filter is configured, it is recommended to rebuild the initrd with mkinitrd (CentOS/RHEL 4 and 5) or dracut (CentOS/RHEL 6 and 7 ) so that only the necessary devices are scanned upon reboot.
Case 2: The two devices displayed in the output are both multipath maps
Example:
Found duplicate PV GDjTZf7Y03GJHjteqOwrye2dcSCjdaUi: using **/dev/mapper/mpatha** not **/dev/mapper/mpathc**
Or
Found duplicate PV GDjTZf7Y03GJHjteqOwrye2dcSCjdaUi: using **/dev/emcpowera** not **/dev/emcpowerh**
Here, we are not looking at two different paths but two different devices. This is a lot more serious than the case above as it often means that the machine has been presented devices which it shouldn’t be seeing (for example, LUN clones or mirrors). In this case, unless you have a clear idea of what devices should be removed from the machine, the situation could be unrecoverable.