[linux-lvm] Read LVM structure of a virtual machine disk image

[Matteo Lanati]

Hi all,

I have a file containing a disk image of a virtual machine. One of the partitions is LVM.
I would like to read the information in there (i.e. the volume group name or the list of logical volumes) from the file itself without exposing the device through kpartx and/or qemu-nbd.
My problem is that on the same physical host I could have multiple copies of the same virtual machine running, using same VGs and LVs. Even the UUID would be the same, hence the impossibility to distinguish the two virtual machines anymore.
Of course, if I could check beforehand the structure of the disk image I could take a different decision and avoid errors.
Thanks,

Matteo


A refund for defective software might be nice, except it would bankrupt the entire software industry in the first year.

Andrew S. Tanenbaum, Computer Networks, 2003, Introduction, page 14

Linux registered user #463400

[Zdenek Kabelac]

Post by Matteo Lanati
Hi all,
I have a file containing a disk image of a virtual machine. One of the partitions is LVM.
I would like to read the information in there (i.e. the volume group name or the list of logical volumes) from the file itself without exposing the device through kpartx and/or qemu-nbd.
My problem is that on the same physical host I could have multiple copies of the same virtual machine running, using same VGs and LVs. Even the UUID would be the same, hence the impossibility to distinguish the two virtual machines anymore.
Of course, if I could check beforehand the structure of the disk image I could take a different decision and avoid errors.
Thanks,

That's why there is a 'filter' setting in your lvm.conf.

You may set different device filter for each lvm command.

You could either use '--config' option with each lvm command where you set
your filter to view only given device - or eventually with latest versions you
may try to use profiles.

It's a users' fault to pass multiple same devices to lvm - it's mandatory to
use different UUIDs, and it's upto user to choose how to achieve it. There is
no way for lvm2 to resolve this inconsistency in come 'always-be-smart' way...

Zdenek

[Matteo Lanati]

Hi Zdenek,

thanks a lot for your input, I would have never figure that out by myself ;-)
All the best,

Matteo




A refund for defective software might be nice, except it would bankrupt the entire software industry in the first year.

Andrew S. Tanenbaum, Computer Networks, 2003, Introduction, page 14

Linux registered user #463400