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

["Alexander Zeidler" <a.zeidler@proxmox.com>]

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@proxmox.com>
> ---
Two formatting suggestions inline, otherwise consider this:
Reviewed-by: Alexander Zeidler <a.zeidler@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).

>  
>  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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