Re: [pve-devel] [PATCH-SERIES v6 pve-storage/qemu-server/pve-qemu] add external qcow2 snapshot support - joao.sousa--- via pve-devel

From: "joao.sousa--- via pve-devel" <pve-devel@lists.proxmox.com>
To: "DERUMIER, Alexandre" <alexandre.derumier@groupe-cyllene.com>,
	 "pve-devel@lists.proxmox.com" <pve-devel@lists.proxmox.com>
Cc: "joao.sousa@eurotux.com" <joao.sousa@eurotux.com>
Subject: Re: [pve-devel] [PATCH-SERIES v6 pve-storage/qemu-server/pve-qemu] add external qcow2 snapshot support
Date: Fri, 13 Jun 2025 17:42:13 +0100	[thread overview]
Message-ID: <mailman.376.1749832968.395.pve-devel@lists.proxmox.com> (raw)
In-Reply-To: <a7185aa585b414710be6e09729adda57ed3787b8.camel@groupe-cyllene.com>

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From: "joao.sousa@eurotux.com" <joao.sousa@eurotux.com>
To: "DERUMIER, Alexandre" <alexandre.derumier@groupe-cyllene.com>,  "pve-devel@lists.proxmox.com" <pve-devel@lists.proxmox.com>
Subject: Re: [pve-devel] [PATCH-SERIES v6 pve-storage/qemu-server/pve-qemu] add external qcow2 snapshot support
Date: Fri, 13 Jun 2025 17:42:13 +0100
Message-ID: <qss36oltvd4gz5tiss7dqono5h2zmsgwmodj4cqkroboizypwj@kbyz3mymh75a>

On 12/06/25 11:33, DERUMIER, Alexandre wrote:
> here the patch series:
> https://lists.proxmox.com/pipermail/pve-devel/2024-August/065201.html
Thanks I'll definitely be checking it out.

> The idea is to create a lvm volume smaller than the real qcow2 size,
>
> qemu is sending an event when the used space reach a threshold,
>
> then a daemon should resize the lvm volume by increment.(1GB for
> example),
> until the next threshold reach....

I was thinking the same way (probably influenced by oVirt's way of
achieving this)

> The only complex thing is to manage some kind of queue in this daemon
> and manage
> lvm cluster lock, as we can't resize multiple lvm volume at the same
> time.
> (Not sure if it need a central daemon, or a distributed daemon on each
> node with a shared queue in /etc/pve ...)

The solution that makes the most sense to me at the moment would be a
"distributed daemon", as in a daemon running on each node of the
cluster. Each node would maintain its own local queue for disk extends
related to the VMs hosted there. When an extend is needed, the node would
acquire the storage lock, perform the task, and then release the lock
so other nodes can proceed with their operations.

What are your thoughts on this approach?

The help is much appreciated :)

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