[pve-devel] [PATCH docs] qm, vzdump: add notes regarding backups of windows and VSS

[Alexander Zeidler]

On Tue Jan 21, 2025 at 3:46 PM CET, Aaron Lauterer wrote:
>
>
> On  2025-01-21  13:08, Alexander Zeidler wrote:
>> On Mon Jan 20, 2025 at 3:35 PM CET, Aaron Lauterer wrote:
>>> VSS in windows guests with additional backup software in the guest can
>>> cause problems. By now the guest agent does support to use a different
>>> VSS option. This way, one can switch to one that does not interfere with
>>> other backup solutions.
>>>
>>> Mention it in the docs and link to the wiki article that explains it.
>>>
>>> Signed-off-by: Aaron Lauterer <a.lauterer at proxmox.com>
>>> ---
>> Two formatting suggestions inline, otherwise consider this:
>> Reviewed-by: Alexander Zeidler <a.zeidler at proxmox.com>
>> 
>>>   qm.adoc     | 13 +++++++++----
>>>   vzdump.adoc |  4 ++++
>>>   2 files changed, 13 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/qm.adoc b/qm.adoc
>>> index 4bb8f2c..660047a 100644
>>> --- a/qm.adoc
>>> +++ b/qm.adoc
>>> @@ -1355,14 +1355,19 @@ that calling 'fs-freeze' with some SQL Servers triggers VSS to call the SQL
>>>   Writer VSS module in a mode that breaks the SQL Server backup chain for
>>>   differential backups.
>>>   
>>> -For such setups you can configure {pve} to not issue a freeze-and-thaw cycle on
>>> +There are two options on how to handle such a situation.
>>> +
>>> +1. Configure the QEMU Guest Agent to use a different VSS variant that does not
>>> +interfere with other VSS users. The https://pve.proxmox.com/wiki/VM_Backup_Consistency[{pve} wiki]
>>> +has more details.
>>> +2. Alternatively, you can configure {pve} to not issue a freeze-and-thaw cycle on
>>>   backup by setting the `freeze-fs-on-backup` QGA option to `0`. This can also be
>>>   done via the GUI with the 'Freeze/thaw guest filesystems on backup for
>>>   consistency' option.
>>>   
>>> -IMPORTANT: Disabling this option can potentially lead to backups with inconsistent
>>> -filesystems and should therefore only be disabled if you know what you are
>>> -doing.
>>> +IMPORTANT: Disabling this option can potentially lead to backups with
>>> +inconsistent filesystems. Therefore, adapting the QEMU Guest Agent
>>> +configuration in the guest is the preferred option.
>> Since there is now a numbered list, it may make sense to move the
>> modified "Important" admonition to option 2 (so indented).
>
> Do you have a suggestion how we can get it indented? I tried getting it 
> into the list item, but that didn't work and I am currenlty not aware 
> how to indent a Note/warning etc.
Sorry! Yes, you can use:
2. [...]
+
IMPORTANT: [...]

>
>> 
>>>   
>>>   Troubleshooting
>>>   ^^^^^^^^^^^^^^^
>>> diff --git a/vzdump.adoc b/vzdump.adoc
>>> index aecb353..0708d07 100644
>>> --- a/vzdump.adoc
>>> +++ b/vzdump.adoc
>>> @@ -96,6 +96,10 @@ a background QEMU process, a stopped VM will appear as running for a
>>>   short amount of time while the VM disks are being read by QEMU.
>>>   However the VM itself is not booted, only its disk(s) are read.
>>>   
>>> +NOTE: On Windows guests it is necessary to configure the guest agent if another
>>> +backup software is used within the guest. See xref:qm_qga_fsfreeze[Freeze & Thaw]
>>> +in the guest agent section for more details.
>> For me it seems more appropriate to put the new note under "snapshot
>> mode" (so indented), since it is only relevant there.
>> 
>>> +
>>>   .Backup modes for Containers:
>>>   
>>>   `stop` mode::
>> 
>> 
>> 
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>> 
>>