[PVE-User] qcow2 vs raw format

Stefan Reiter s.reiter at proxmox.com
Mon Mar 9 14:55:52 CET 2020


On 3/9/20 2:37 PM, Laurent Dumont wrote:
> I'm not sure if this still stands but you cannot do snapshots on a raw
> format, only qcow2.

Correct, but note that this only applies to file-based raw storage, a 
"raw" volume on lvm-thin, ZFS, etc. does of course support snapshots.

On file-based storages, qcow2 does indeed give you the benefit of 
snapshots over raw images, but comes with a slight overhead - usually 
negligible IMHO and from my experience, but that's something you should 
test yourself with your own workload if you need it.

> 
> On Mon, Mar 9, 2020, 9:35 AM Leandro Roggerone <leandro at tecnetmza.com.ar>
> wrote:
> 
>> Is there any reason to use qcow2 format ?
>> Im asking because I received qcow2 disk from an old system and need to
>> upload into my new pve.

FYI: You can use 'qm importdisk' to attach existing disk images to a VM. 
This also allows to import qcow2 images to storages not supporting qcow2 
as a format, e.g. LVM, ZFS, ...

>> I just want to know why people used this, my system currently does not
>> support it.
>> Leandro.
>>
>> <
>> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail
>>>
>> Libre
>> de virus. www.avast.com
>> <
>> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail
>>>
>> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>>
>> El lun., 9 mar. 2020 a las 10:27, Laurent Dumont (<
>> laurentfdumont at gmail.com>)
>> escribió:
>>
>>> This server fault post was written in 2012. I will do some test in the
>> lab
>>> but those results seem really really low for a modern system with modern
>>> packages.
>>>
>>> On Mon, Mar 9, 2020, 9:21 AM Roland @web.de <devzero at web.de> wrote:
>>>
>>>>   >Performance-wise, they should be almost the same. qcow2 is a bit more
>>>> complex than a raw file/partition, but I don't think you'll notice any
>>>> impact.
>>>>
>>>> i did test that a while ago and got very different results, qcow2 was
>>>> much slower on my system. cannot provide details, though (did not save
>>>> that)
>>>>
>>>> i recommend reading
>>>>
>>>>
>>>
>> https://serverfault.com/questions/407842/incredibly-low-kvm-disk-performance-qcow2-disk-files-virtio
>>>> and compare yourself....
>>>>
>>>> roland
>>>>
>>>> Am 09.03.20 um 13:35 schrieb Eneko Lacunza:
>>>>> Hola Leandro,
>>>>>
>>>>> El 9/3/20 a las 13:21, Leandro Roggerone escribió:
>>>>>> Thankyou Eneko ,
>>>>>> Are features / performance difference between those formats ?
>>>>>
>>>>> Take a look at:
>>>>> https://pve.proxmox.com/wiki/Storage
>>>>>
>>>>> Performance-wise, they should be almost the same. qcow2 is a bit more
>>>>> complex than a raw file/partition, but I don't think you'll notice
>> any
>>>>> impact. Maybe others can comment on this.
>>>>>
>>>>> Saludos
>>>>> Eneko
>>>>>
>>>>>> Regards,
>>>>>> Leandro.
>>>>>>
>>>>>> <
>>>>
>>>
>> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail
>>>>>
>>>>>>
>>>>>> Libre
>>>>>> de virus. www.avast.com
>>>>>> <
>>>>
>>>
>> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail
>>>>>
>>>>>>
>>>>>> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>>>>>>
>>>>>> El lun., 9 mar. 2020 a las 9:17, Eneko Lacunza (<elacunza at binovo.es
>>> )
>>>>>> escribió:
>>>>>>
>>>>>>> Hola Leandro,
>>>>>>>
>>>>>>> El 9/3/20 a las 13:11, Leandro Roggerone escribió:
>>>>>>>> Hi guys, after install pve , would like to create my first VM.
>>>>>>>> I noticed that only available format is raw.
>>>>>>>> Question is:
>>>>>>>> Is qcow2 deprecated ?
>>>>>>>> What are differences between them ? (I already google it but is
>> not
>>>>>>>> 100%
>>>>>>>> clear).
>>>>>>>>
>>>>>>>> This is my storage configuration is.
>>>>>>>> root at pve:~# cat /etc/pve/storage.cfg
>>>>>>>> dir: local
>>>>>>>>            path /var/lib/vz
>>>>>>>>            content iso,vztmpl,backup
>>>>>>>>
>>>>>>>> lvmthin: local-lvm
>>>>>>>>            thinpool data
>>>>>>>>            vgname pve
>>>>>>>>            content rootdir,images
>>>>>>>>
>>>>>>> You need a file-type storage (i.e. dir type) to be able to use
>> qcow2
>>>>>>> format. Default local-lvm is lvmthin and only logical volumes in
>> raw
>>>>>>> format can be created (no raw files are created in fact).
>>>>>>>
>>>>>>> Cheers
>>>>>>> Eneko
>>>>>>>
>>>>>>> --
>>>>>>> Zuzendari Teknikoa / Director Técnico
>>>>>>> Binovo IT Human Project, S.L.
>>>>>>> Telf. 943569206
>>>>>>> Astigarragako bidea 2, 2º izq. oficina 11; 20180 Oiartzun
>> (Gipuzkoa)
>>>>>>> www.binovo.es
>>>>>>>
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>>
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