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qm, vzdump: add notes regarding backups of windows and VSS

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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>
Reviewed-by: Alexander Zeidler <a.zeidler@proxmox.com>
This commit is contained in:
Aaron Lauterer 2025-01-20 15:32:57 +01:00
parent 0c2dcfce35
commit 2c12c2b1d5
2 changed files with 14 additions and 5 deletions
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15
qm.adoc
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@ -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.
Troubleshooting
^^^^^^^^^^^^^^^

4
vzdump.adoc
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@ -84,6 +84,10 @@ backup, in which data blocks are copied while the VM is running. If the
guest agent is enabled (`agent: 1`) and running, it calls
`guest-fsfreeze-freeze` and `guest-fsfreeze-thaw` to improve
consistency.
+
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.
A technical overview of the {pve} live backup for QemuServer can
be found online