TheLazy.Dev
Portfolio GitHub

Blog

lvm |linux |mount

How to mount a lvm volume which is inside a lvm volume

c33s

Julian

Posted on November 12, 2019

How to mount a lvm volume which is inside a lvm volume

if you use something like kvm for virtualization and also use lvm on the host system a good practice is to create a volume for each virtual machine.

to don't make a difference between a physical system and a virtual system, i like to also use lvm in the virtual systems. it works like charm but mounting a volume from virtual machine is kind of tricky. it's getting even trickier if your volume groups all have the same names.

kvm host:
    vg_main:
        home
        tmp
        ...
        kvm_web01
            vg_main:
                home
                tmp
                ...
Enter fullscreen mode Exit fullscreen mode

so if you try to mount kvm_web01 directly you get an error:

mount /dev/mapper/vg_main-kvm_web01  /mnt/web01/
mount: /mnt/web01: wrong fs type, bad option, bad superblock on /dev/mapper/vg_main-kvm_web01, missing codepage or helper program, or other error.
Enter fullscreen mode Exit fullscreen mode

with kpartx (aptitude install kpartx) you can detect partitions inside of an lvm volume and make them accessible:

kpartx -av /dev/mapper/vg_main-kvm_web01
add map vg_main-kvm_web01p1 (253:16): 0 389120 linear 253:7 2048
add map vg_main-kvm_web01p2 (253:17): 0 2 linear 253:7 393214
add map vg_main-kvm_web01p5 (253:18): 0 83490816 linear 253:7 393216
Enter fullscreen mode Exit fullscreen mode

now the partitions are accessible. you can mount the non lvm boot partition vg_main-kvm_web01p1 but you still get an error if you try to mount the physical volume on partition vg_main-kvm_web01p2

mount: ....  unknown filesystem type 'LVM2_member'.
Enter fullscreen mode Exit fullscreen mode

(this message is not 100% accurate because i already finished the recovery and i am reproducing the steps without redoing all again)

with pvscan the partition made visible with kpartx are now also known by lvm.

pvscan
vgdisplay
Enter fullscreen mode Exit fullscreen mode

in my case i ran in the next problem of having two volume groups with the same name vg_main. lvs gave the correct output with most of the partitions duplicated

lvs
root@zhaan ~ # lvs
  LV             VG      Attr     LSize   Pool Origin Data%  Move Log Copy%  Convert
  home           vg_main -wi-ao--   1.00g
  home           vg_main -wi-ao--   2.00g
...
Enter fullscreen mode Exit fullscreen mode

so you use vgdisplay to find out the id of the inner volume group (should be the one with less harddisk space) and vgrename to rename it.

vgrename -v 6FW1tp-aeVy-1oTW-Ho1M-DwV7-TPB0-QCIoz4 vg_web01
    Cache: Duplicate VG name vg_main: Existing 306MGq-WfN8-LFx5-SKvw-uIfv-dSj0-QCSfGT (created here) takes precedence over 6FW1tp-aeVy-1oTW-Ho1M-DwV7-TPB0-QCIoz4
  Processing VG vg_main because of matching UUID 6FW1tp-aeVy-1oTW-Ho1M-DwV7-TPB0-QCIoz4
    Cache: Duplicate VG name vg_main: Existing 306MGq-WfN8-LFx5-SKvw-uIfv-dSj0-QCSfGT (created here) takes precedence over 6FW1tp-aeVy-1oTW-Ho1M-DwV7-TPB0-QCIoz4
    Archiving volume group "vg_main" metadata (seqno 8).
    Writing out updated volume group
    Renaming "/dev/vg_main" to "/dev/vg_web01"
    Creating volume group backup "/etc/lvm/backup/vg_web01" (seqno 9).
  Volume group "6FW1tp-aeVy-1oTW-Ho1M-DwV7-TPB0-QCIoz4" successfully renamed to "vg_web01"
Enter fullscreen mode Exit fullscreen mode

and the use vgchange to "refresh" the logical volume list:

vgchange -a y
  6 logical volume(s) in volume group "vg_web01" now active
  16 logical volume(s) in volume group "vg_main" now active
Enter fullscreen mode Exit fullscreen mode

then you simply use mount to make it accessible on your host system:

mount /dev/vg_web01/home /mnt/web01/home
Enter fullscreen mode Exit fullscreen mode

lvm rocks! :)

(hope i put my notes together correct. if you find an error trying it out, please comment)

links:

💖 💪 🙅 🚩
c33s
Julian

Posted on November 12, 2019

Join Our Newsletter. No Spam, Only the good stuff.

Sign up to receive the latest update from our blog.

Related

How to mount a lvm volume which is inside a lvm volume
lvm How to mount a lvm volume which is inside a lvm volume

November 12, 2019