multipath_component_detection = 0 in lvm.conf does not have any effect

[tangophi]

Description of problem:

Disabling multipath component detection in lvm.conf does not have any effect. It always ignores PVs on native devices irrespective of whether multipath component detection is enabled or not.

We have a specific requirement for lvm to NOT ignore PVs on multiple native devices when dm-multipath is NOT enabled.

Version-Release number of selected component (if applicable):

With RHEL 9:
lvm2-libs-2.03.14-4.el9.x86_64
lvm2-2.03.14-4.el9.x86_64

How reproducible:

Every time.

Steps to Reproduce:

1. Disable both the use of devices file and multipath component detection in /etc/lvm/lvm.conf by setting the following.

use_devicesfile = 0
multipath_component_detection = 0

2. Create a PV on one path of a native device to an array LUN.

[root@ncpp227046 ~]# pvcreate /dev/sdci
  Physical volume "/dev/sdci" successfully created.

3. Run pvscan to see the just created PV.

[root@ncpp227046 ~]# pvscan
  PV /dev/sdh3   VG rhel_ncpp227046   lvm2 [53.41 GiB / 0    free]
  Total: 1 [53.41 GiB] / in use: 1 [53.41 GiB] / in no VG: 0 [0   ]

The PV shown above is a different PV on the local hard disk. It does not show the PV on the just created device.

Actual results:

pvscan does not show the PV on a native device. Here, /dev/sdci, /dev/sddc and /dev/sdbk are all paths to the same array LUN.

As seen below from the snippet of 'pvscan -vvv' output, lvm ignores all the native devices as it sees duplicate PVIDs on them. It does this because it believes there will be a dm-multipath device also available - but in our case there will not be any dm-multipath device as dm-multipath is not enabled (as multipathing will be provided with another software).

  Resolving duplicate devices
  Checking for multipath components for duplicate PVID fNvc7okgiFdvF1ociAUMMGwhic5rfHxL
  Same wwids for duplicate PVs /dev/sdci /dev/sddc
  Same wwids for duplicate PVs /dev/sdci /dev/sdbk
  Ignoring multipath component /dev/sdci with PVID fNvc7okgiFdvF1ociAUMMGwhic5rfHxL (dropping info)
  Ignoring multipath component /dev/sddc with PVID fNvc7okgiFdvF1ociAUMMGwhic5rfHxL (dropping duplicate)
  Ignoring multipath component /dev/sdbk with PVID fNvc7okgiFdvF1ociAUMMGwhic5rfHxL (dropping duplicate)

Expected results:

pvscan should have shown /dev/sdci and duplicate PVs on /dev/sddc and /dev/sdbk. Essentially we require a similar behavior as in older LVM versions (such as in RHEL 8).

[tangophi]

https://sourceware.org/git/?p=lvm2.git;a=commit;h=99ce09ae778c2cc4aa2611e425bba5287b8b9513

Issue has been fixed with the above commit. Hence closing.