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

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

[Fiona Ebner]

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
-- 
2.47.3

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

[Maximiliano Sandoval]

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

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

[Thomas Lamprecht]

On Mon, 23 Mar 2026 12:06:25 +0100, Fiona Ebner wrote:
> 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.
> 
> 

Not 100% sure if this is the best place for this info, but it's not the wrong
place, it's central and from top of my head I do not have a better idea, so
probably fine..

Applied, thanks!

[1/1] storage: note that qcow2 internal snapshots are inefficient
      commit: 0bb63fb9b322a33d0f2f28cc49b2dbb9adad5c48