[PVE-User] Using raw LVM without partitions inside VM

[Brian Hart]

Hello everybody,

For a long time now I've used raw LVM on disks inside of virtual machines
without using disk partitions.  I create a separate small disk to serve for
the "boot" drive and give it a partition.  This is formatted and mounted in
/boot.  Then we create a separate disk to contain everything else in an LVM
structure.  Outside of Proxmox this is perfectly acceptable as long as you
do not need to boot from the device which we do not since we create that
separate device.  The partition table would only serve as a method for the
bios to interact with the disk for boot purposes.  The main advantage here
is it makes the non-boot sections of the system very fluid and makes adding
removing space on a live system SO much easier without having to worry
about the restrictions of a partition table.

We've been doing this successfully in VMware for a long time but only today
did we attempt this in Proxmox and ran into a serious issue which long
story short - resulted in the loss of a disk.  I understand what went wrong
and why this happened and luckily it was just a template that it happened
to so nothing major lost, we can rebuild it.  On Proxmox we use an iSCSI
SAN with multipath connections for our backend storage so we do LVM on
proxmox for our disks for our VMs.  I know some answers on the forum are to
"use partitions" and I understand why that is the answer given but we do
this very intentionally with a deep understanding of how it would normally
work.  The reason it doesn't is because of how the disks are handled on LVM
backed storage on the host in this case.

What I am hoping for are alternate suggestion on how we can use raw LVM on
disks with proxmox?  Do we need to use a different storage method?  Would
this same problem exist some how with qcow2 files or on a ZFS backed
storage (such as ZFS over iSCSI)?  It seems like it shouldn't for the same
reasons it doesn't happen on VMware with VMDK files but I wanted to be
sure.  If I understand the issue correctly it should only be because we're
doing LVM on a raw block device and so the proxmox host sees that
directly.  I would expect something like a qcow2 file would sufficiently
shield it but maybe not the ZFS over iSCSI(?)  I'm not sure.  I'm basically
looking for any creative solutions to accomplish what we are trying to do
or any advice that doesn't follow the beaten path of "use partitions".

Thanks for any feedback or suggestions --

Brian
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