RHEL7: A race between devices appearing on boot, and lvm volumes not becoming usable

Solution Verified - Updated -

Issue

  • A race between FCoE devices appearing and lvm2-activation-net.service running
  • FCoE LUNs get not assembled into volume groups when booted. There are two volumes groups, and they should be assembled by systemd and then mounted. When booting we see that the job for them runs and (not shown) times out:
(1 of 2) A start job is running for dev-disk-by\x2duuid-3db...\x2d4ec8\x2d8042\x2dc514dee7b723.device (38s / 1min 30s)
(1 of 2) A start job is running for dev-disk-by\x2duuid-3db...\x2d4ec8\x2d8042\x2dc514dee7b723.device (39s / 1min 30s)
(1 of 2) A start job is running for dev-disk-by\x2duuid-3db...\x2d4ec8\x2d8042\x2dc514dee7b723.device (40s / 1min 30s)
(2 of 2) A start job is running for dev-disk-by\x2duuid-58f...\x2d4e8c\x2dade4\x2daebf54c94abe.device (40s / 1min 30s)

Upon boot the volume group can be seen but it's not activated:

/dev/mapper/mpathf1 VG01 lvm2 a--  <50g  0 49.98g k436Le-kKY3-Tu3f-BcyH-qvSH-ZzcP-Pd6W9P    <8.00m   <16.00m   1    1  16.00m
/dev/mapper/mpathg1 VG02 lvm2 a--  <70g  0 69.98g pfpEoz-OF2n-t3n4-uCHh-N12j-aVlD-dfzC2l    <8.00m   <16.00m   1    1  16.00m

They each have one LogicalVolume (LV):

LV01      VG01 -wi------- <49.97g         /dev/mapper/mpathf1(0)
LV01      VG02 -wi------- <69.97g         /dev/mapper/mpathg1(0)

The sosreport shows that the LV is not active. From the sosreport, we can see this order:

  • The FCoE driver is loaded, devices start appearing. The fcoe.service completes, but the driver continues asynchronously to detect LUNs.
  • The lvm2-activation-net.service runs, it is running vgscan, which is looking at the devices known to the system and analyses whether they have LVM signatures. Not all LUNs which are part of the VolumeGroup have at that point been detected, the lvm2-activation-net.service thus can not assemble the volumes, it finishes.
  • At some point later, the detection of FCoE LUNs finishes, no new LUNs are appearing any more.

Environment

  • Red Hat Enterprise Linux (RHEL) 7
  • SAN, FCoE, iSCSI or other backends providing LUNs
  • LogicalVolumeManager (LVM)
    • PhysicalVolume (PV, the lowest layer, a unit directly living on a blockdevice)
    • VolumeGroup (VG, spanning at least one PV)
    • LogicalVolume (LV, multiple LV's can be part of one VG)

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