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

[Aaron Lauterer]

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.

> 
>>   
>>   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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