[linux-lvm] convert LV to physical device _in_place_?

Stuart Gathman stuart at gathman.org
Fri Jul 14 03:41:12 UTC 2017

On 07/13/2017 09:25 AM, Matthias Leopold wrote:
> i'm fiddling around with LVM backed KVM raw disks, that i want to use
> _directly_ in oVirt virtualization (as "Direct LUN"). i would like to
> avoid "importing", dd, etc. if possible. in the KVM origin system
> exists a mapping of one iSCSI whole device (no partitions) to one PV
> to one VG to one LV per KVM disk. i can now present these iSCSI
> devices to the oVirt hosts, where i can only use them as "Direct LUN"
> without the LVM layer (i guess). so all i would need is to remove the
> LVM metadata from the iSCSI device preserving the "content" of the LV.
> pvremove seems to be too "intrusive" for this... i know this sounds
> rather naive and i didn't find any recipes for it. everybody talks
> about dd to a new device, which of course works (i tried it), but is
> exactly what i want to avoid when migrating very large disks (TB). i
> hope someone understands my concern and maybe has a solution
I use iSCSI at home, and I just export the LV as an iSCSI target.  Now
you have direct LUN for use with VM hosts on the network (I just have a
gigabit LAN at home).  The iSCSI server still uses LVM, and you can
snapshot the volume for backup on the server.

Maybe that's too obvious, and I misunderstood your problem?

There is no LVM metatdata on the exported iSCSI devices - that is on the
underlying disk.  As the export LUN looks like a disk, you can even add
an optional partition table, PVs, VGs, etc for use by the virtual machine.

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