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
...
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.
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
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'.
(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
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
...
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"
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
then you simply use mount to make it accessible on your host system:
mount /dev/vg_web01/home /mnt/web01/home
lvm rocks! :)
(hope i put my notes together correct. if you find an error trying it out, please comment)
links:
- cover image by jackmac34 https://pixabay.com/photos/matryoshka-russian-dolls-nesting-970943/
- https://stackoverflow.com/questions/14048965/how-to-mount-a-lvm-partition-within-a-lvm-volume
- https://unix.stackexchange.com/questions/339011/how-do-i-mount-an-lvm-partition
- https://documentation.online.net/en/dedicated-server/rescue/mount-lvm-partition
- https://askubuntu.com/questions/110226/how-do-you-mount-a-lvm-patition-that-has-the-same-vg-name-as-my-current-partitio
- https://pissedoffadmins.com/os/mount-unknown-filesystem-type-lvm2_member.html
- https://askubuntu.com/questions/766048/mount-unknown-filesystem-type-lvm2-member
Top comments (3)
Well done - thank you!
is that possible to snapshot inside a lvm ? is that any way to mount that snapshot inside a lvm?
Thank you!