Re: [pve-devel] [PATCH docs] storage: note that qcow2 internal snapshots are inefficient

[Maximiliano Sandoval <m.sandoval@proxmox.com>]

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

> Am 28.11.25 um 4:56 PM schrieb Fiona Ebner:
>> It's a commonly reported issue, most recently again 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>
>> ---
>>  pvesm.adoc | 5 +++++
>>  1 file changed, 5 insertions(+)
>> 
>> diff --git a/pvesm.adoc b/pvesm.adoc
>> index d36baf8..165b446 100644
>> --- a/pvesm.adoc
>> +++ b/pvesm.adoc
>> @@ -88,6 +88,11 @@ 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.
>>  
>>  ^3^: It is possible to use LVM on top of an iSCSI or FC-based storage.
>>  That way you get a `shared` LVM storage
>
> Ping

In my experience, users mostly into issues when deleting qcow2 snapshots
on NFS can take up to 10 hours. I would personally put more emphasis on
this specific combination being problematic, and probably mention that
in such case one should delete snapshots while the VM is offline.

-- 
Maximiliano