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Have been trying to mount QEMU image with qcow2 type on Fedora 20 host, according to this article http://docs.openstack.org/image-guide/content/ch_modifying_images.html It appears that 'vgscan' doesn't see partitions on /dev/nbd0 where I linked to my image:

% vgscan -vvv
      Setting activation/monitoring to 1
        Processing: vgscan -vvv
        O_DIRECT will be used
      Setting global/locking_type to 1
      Setting global/wait_for_locks to 1
      File-based locking selected.
      Setting global/locking_dir to /run/lock/lvm
      Setting global/prioritise_write_locks to 1
      Locking /run/lock/lvm/P_global WB
        _do_flock /run/lock/lvm/P_global:aux WB
        _do_flock /run/lock/lvm/P_global WB
        _undo_flock /run/lock/lvm/P_global:aux
        Metadata cache has no info for vgname: "#global"
    Wiping cache of LVM-capable devices
        /dev/sda: Added to device cache
        /dev/disk/by-id/ata-WDC_WD10EZEX-75M2NA0_WD-WCC3F4935054: Aliased to /dev/sda in device cache
        /dev/disk/by-id/wwn-0x50014ee25f867e03: Aliased to /dev/sda in device cache
        /dev/sda1: Added to device cache
        /dev/disk/by-id/ata-WDC_WD10EZEX-75M2NA0_WD-WCC3F4935054-part1: Aliased to /dev/sda1 in device cache
        /dev/disk/by-id/wwn-0x50014ee25f867e03-part1: Aliased to /dev/sda1 in device cache
        /dev/disk/by-uuid/1c1a9d75-070a-4c5b-8d66-24cae1141dd7: Aliased to /dev/sda1 in device cache
        /dev/sda2: Added to device cache
        /dev/disk/by-id/ata-WDC_WD10EZEX-75M2NA0_WD-WCC3F4935054-part2: Aliased to /dev/sda2 in device cache
        /dev/disk/by-id/lvm-pv-uuid-DnkMt8-bu1E-7dJo-Sdcc-GlT6-sKec-FjFj1o: Aliased to /dev/sda2 in device cache
        /dev/disk/by-id/wwn-0x50014ee25f867e03-part2: Aliased to /dev/sda2 in device cache
        /dev/sr0: Added to device cache
        /dev/cdrom: Aliased to /dev/sr0 in device cache (preferred name)
        /dev/disk/by-id/ata-ASUS_DRW-24F1ST_a_S10K68EF300J0B: Aliased to /dev/cdrom in device cache
        /dev/nbd0: Added to device cache
        /dev/nbd0p1: Added to device cache
        /dev/nbd0p2: Added to device cache
        /dev/nbd1: Added to device cache
        /dev/nbd10: Added to device cache
        /dev/nbd11: Added to device cache
        /dev/nbd12: Added to device cache
        /dev/nbd13: Added to device cache
        /dev/nbd14: Added to device cache
        /dev/nbd15: Added to device cache
        /dev/nbd2: Added to device cache
        /dev/nbd3: Added to device cache
        /dev/nbd4: Added to device cache
        /dev/nbd5: Added to device cache
        /dev/nbd6: Added to device cache
        /dev/nbd7: Added to device cache
        /dev/nbd8: Added to device cache
        /dev/nbd9: Added to device cache
        /dev/dm-0: Added to device cache
        /dev/disk/by-id/dm-name-fedora_nfv--s1-swap: Aliased to /dev/dm-0 in device cache (preferred name)
        /dev/disk/by-id/dm-uuid-LVM-KisoyqxG0iu1uFiZsLL7nVSSX0Ow8qwTYdLBLM9aOVskeq2PlKwTefSpNK2tdqi2: Aliased to /dev/disk/by-id/dm-name-fedora_nfv--s1-swap in device cache
        /dev/disk/by-uuid/fd91acd1-1ff8-4db9-a070-f999a387489c: Aliased to /dev/disk/by-id/dm-name-fedora_nfv--s1-swap in device cache
        /dev/fedora_nfv-s1/swap: Aliased to /dev/disk/by-id/dm-name-fedora_nfv--s1-swap in device cache (preferred name)
        /dev/mapper/fedora_nfv--s1-swap: Aliased to /dev/fedora_nfv-s1/swap in device cache
        /dev/dm-1: Added to device cache
        /dev/disk/by-id/dm-name-fedora_nfv--s1-root: Aliased to /dev/dm-1 in device cache (preferred name)
        /dev/disk/by-id/dm-uuid-LVM-KisoyqxG0iu1uFiZsLL7nVSSX0Ow8qwTQy5rPQnLskMuc0luyn5HeUAJcC4sHz0t: Aliased to /dev/disk/by-id/dm-name-fedora_nfv--s1-root in device cache
        /dev/disk/by-uuid/44fd9e97-274d-4536-b8f2-9a0d6e33a33a: Aliased to /dev/disk/by-id/dm-name-fedora_nfv--s1-root in device cache
        /dev/fedora_nfv-s1/root: Aliased to /dev/disk/by-id/dm-name-fedora_nfv--s1-root in device cache (preferred name)
        /dev/mapper/fedora_nfv--s1-root: Aliased to /dev/fedora_nfv-s1/root in device cache
        /dev/dm-2: Added to device cache
        /dev/disk/by-id/dm-name-fedora_nfv--s1-home: Aliased to /dev/dm-2 in device cache (preferred name)
        /dev/disk/by-id/dm-uuid-LVM-KisoyqxG0iu1uFiZsLL7nVSSX0Ow8qwTtNmpzJ9SfcvKnnvdlfdseL6QLUnvP5vA: Aliased to /dev/disk/by-id/dm-name-fedora_nfv--s1-home in device cache
        /dev/disk/by-uuid/c6b30418-b427-430d-916b-dceb4d08b5d9: Aliased to /dev/disk/by-id/dm-name-fedora_nfv--s1-home in device cache
        /dev/fedora_nfv-s1/home: Aliased to /dev/disk/by-id/dm-name-fedora_nfv--s1-home in device cache (preferred name)
        /dev/mapper/fedora_nfv--s1-home: Aliased to /dev/fedora_nfv-s1/home in device cache
    Wiping internal VG cache
        Metadata cache has no info for vgname: "#global"
        Metadata cache has no info for vgname: "#orphans_lvm1"
        Metadata cache has no info for vgname: "#orphans_lvm1"
        lvmcache: initialised VG #orphans_lvm1
        Metadata cache has no info for vgname: "#orphans_pool"
        Metadata cache has no info for vgname: "#orphans_pool"
        lvmcache: initialised VG #orphans_pool
        Metadata cache has no info for vgname: "#orphans_lvm2"
        Metadata cache has no info for vgname: "#orphans_lvm2"
        lvmcache: initialised VG #orphans_lvm2
  Reading all physical volumes.  This may take a while...
    Finding all volume groups
        Asking lvmetad for complete list of known VGs
      Setting response to OK
      Setting response to OK
        Asking lvmetad for VG Kisoyq-xG0i-u1uF-iZsL-L7nV-SSX0-Ow8qwT (name unknown)
      Setting response to OK
      Setting response to OK
      Setting name to fedora_nfv-s1
      Setting metadata/format to lvm2
        Metadata cache has no info for vgname: "fedora_nfv-s1"
      Setting id to DnkMt8-bu1E-7dJo-Sdcc-GlT6-sKec-FjFj1o
      Setting format to lvm2
      Setting device to 2050
      Setting dev_size to 1952497664
      Setting label_sector to 1
        /dev/sda2: Device is a partition, using primary device /dev/sda for mpath component detection
        Opened /dev/sda2 RO O_DIRECT
      /dev/sda2: size is 1952497664 sectors
        Closed /dev/sda2
      /dev/sda2: size is 1952497664 sectors
        Opened /dev/sda2 RO O_DIRECT
        /dev/sda2: block size is 4096 bytes
        /dev/sda2: physical block size is 4096 bytes
        Closed /dev/sda2
        lvmcache: /dev/sda2: now in VG #orphans_lvm2 (#orphans_lvm2) with 0 mdas
      Setting size to 1044480
      Setting start to 4096
      Setting ignore to 0
        Allocated VG fedora_nfv-s1 at 0x7f985779d4c0.
        Metadata cache has no info for vgname: "fedora_nfv-s1"
        Metadata cache has no info for vgname: "fedora_nfv-s1"
        lvmcache: /dev/sda2: now in VG fedora_nfv-s1 with 1 mdas
        lvmcache: /dev/sda2: setting fedora_nfv-s1 VGID to KisoyqxG0iu1uFiZsLL7nVSSX0Ow8qwT
        Freeing VG fedora_nfv-s1 at 0x7f985779d4c0.
    Finding volume group "fedora_nfv-s1"
      Locking /run/lock/lvm/V_fedora_nfv-s1 RB
        _do_flock /run/lock/lvm/V_fedora_nfv-s1:aux WB
        _undo_flock /run/lock/lvm/V_fedora_nfv-s1:aux
        _do_flock /run/lock/lvm/V_fedora_nfv-s1 RB
        Asking lvmetad for VG Kisoyq-xG0i-u1uF-iZsL-L7nV-SSX0-Ow8qwT (fedora_nfv-s1)
      Setting response to OK
      Setting response to OK
      Setting name to fedora_nfv-s1
      Setting metadata/format to lvm2
      Setting id to DnkMt8-bu1E-7dJo-Sdcc-GlT6-sKec-FjFj1o
      Setting format to lvm2
      Setting device to 2050
      Setting dev_size to 1952497664
      Setting label_sector to 1
      Setting size to 1044480
      Setting start to 4096
      Setting ignore to 0
        Allocated VG fedora_nfv-s1 at 0x7f98577920b0.
        /dev/sda2 0:      0   2020: swap(0:0)
        /dev/sda2 1:   2020 223521: home(0:0)
        /dev/sda2 2: 225541  12800: root(0:0)
        Allocated VG fedora_nfv-s1 at 0x7f98577960c0.
  Found volume group "fedora_nfv-s1" using metadata type lvm2
        Freeing VG fedora_nfv-s1 at 0x7f985779e0e0.
        Unlock: Memlock counters: locked:0 critical:0 daemon:0 suspended:0
        Syncing device names
      Unlocking /run/lock/lvm/V_fedora_nfv-s1
        _undo_flock /run/lock/lvm/V_fedora_nfv-s1
        Freeing VG fedora_nfv-s1 at 0x7f98577960c0.
        Freeing VG fedora_nfv-s1 at 0x7f98577920b0.
      Unlocking /run/lock/lvm/P_global
        _undo_flock /run/lock/lvm/P_global
        Metadata cache has no info for vgname: "#global"
        Completed: vgscan -vvv
%

vgscan is part of package lvm2-2.02.106-1.fc20.x86_64

I wonder what could be the reason, and what else I should try? Thanks.

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It seems that there does exist a problem in lvm2 package so that pvscan does not run from udev for nbd devices. So as a solution/workaround, one should disable process lvmetad (via systemctl on Fedora as well as set use_lvmetad=0 in /etc/lvm/lvm.conf) before running vgscan.

After that vgscan will find LVM on /dev/nbd* and they can be mounted.

  • You can terminate lvmetad process (by killing) and trying carrying out vgscan, pvscan and lvscan. – kumar Aug 19 '15 at 9:40

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