Re: [PATCH v2 docs] storage: note that qcow2 internal snapshots are inefficient

Maximiliano Sandoval
2026-03-23T12:00:15Z

Fiona Ebner <f.ebner@proxmox.com> writes:

> It's a commonly reported issue, often also in the enterprise support,
> that taking or removing snapshots of large qcow2 files on file-based
> network storages can take a very long time. Add a note about this
> limitation.
>
> Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
> ---
>
> Changes in v2:
> * add recommendation about doing the operations offline
>
> pvesm.adoc | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/pvesm.adoc b/pvesm.adoc
> index c634f6b..97feca0 100644
> --- a/pvesm.adoc
> +++ b/pvesm.adoc
> @@ -88,6 +88,12 @@ block device functionality.
>
> ^2^: On file based storages, snapshots are possible with the 'qcow2' format,
> either using the internal snapshot function, or snapshots as volume chains^4^.
> +Creating and deleting internal 'qcow2' snapshots will block a running VM and
> +is not an efficient operation. The performance is particularly bad with network
> +storages like NFS. On some setups and for large disks (multiple hundred GiB or
> +TiB sized), these operations may take several minutes, or in extreme cases, even
> +hours. If your setup is affected, create and remove snapshots while the VM is
> +shut down, expecting a long task duration.
>
> ^3^: It is possible to use LVM on top of an iSCSI or FC-based storage.
> That way you get a `shared` LVM storage

Looks good to me.

Reviewed-by: Maximiliano Sandoval <m.sandoval@proxmox.com>

--
Maximiliano