From mboxrd@z Thu Jan 1 00:00:00 1970
Return-Path: <c.heiss@proxmox.com>
Received: from firstgate.proxmox.com (firstgate.proxmox.com [212.224.123.68])
(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)
key-exchange X25519 server-signature RSA-PSS (2048 bits))
(No client certificate requested)
by lists.proxmox.com (Postfix) with ESMTPS id 115789436F
for <pve-devel@lists.proxmox.com>; Thu, 23 Feb 2023 15:18:42 +0100 (CET)
Received: from firstgate.proxmox.com (localhost [127.0.0.1])
by firstgate.proxmox.com (Proxmox) with ESMTP id E5F27256B2
for <pve-devel@lists.proxmox.com>; Thu, 23 Feb 2023 15:18:11 +0100 (CET)
Received: from proxmox-new.maurer-it.com (proxmox-new.maurer-it.com
[94.136.29.106])
(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)
key-exchange X25519 server-signature RSA-PSS (2048 bits))
(No client certificate requested)
by firstgate.proxmox.com (Proxmox) with ESMTPS
for <pve-devel@lists.proxmox.com>; Thu, 23 Feb 2023 15:18:11 +0100 (CET)
Received: from proxmox-new.maurer-it.com (localhost.localdomain [127.0.0.1])
by proxmox-new.maurer-it.com (Proxmox) with ESMTP id EA1604829A
for <pve-devel@lists.proxmox.com>; Thu, 23 Feb 2023 15:18:10 +0100 (CET)
From: Christoph Heiss <c.heiss@proxmox.com>
To: pve-devel@lists.proxmox.com
Date: Thu, 23 Feb 2023 15:18:05 +0100
Message-Id: <20230223141805.446192-4-c.heiss@proxmox.com>
X-Mailer: git-send-email 2.39.1
In-Reply-To: <20230223141805.446192-1-c.heiss@proxmox.com>
References: <20230223141805.446192-1-c.heiss@proxmox.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
X-SPAM-LEVEL: Spam detection results: 0
AWL -0.091 Adjusted score from AWL reputation of From: address
BAYES_00 -1.9 Bayes spam probability is 0 to 1%
KAM_DMARC_STATUS 0.01 Test Rule for DKIM or SPF Failure with Strict Alignment
SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record
SPF_PASS -0.001 SPF: sender matches SPF record
Subject: [pve-devel] [PATCH v2 docs 3/3] qm: Add section explaining
fs-freeze/-thaw QGA option
X-BeenThere: pve-devel@lists.proxmox.com
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Proxmox VE development discussion <pve-devel.lists.proxmox.com>
List-Unsubscribe: <https://lists.proxmox.com/cgi-bin/mailman/options/pve-devel>,
<mailto:pve-devel-request@lists.proxmox.com?subject=unsubscribe>
List-Archive: <http://lists.proxmox.com/pipermail/pve-devel/>
List-Post: <mailto:pve-devel@lists.proxmox.com>
List-Help: <mailto:pve-devel-request@lists.proxmox.com?subject=help>
List-Subscribe: <https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel>,
<mailto:pve-devel-request@lists.proxmox.com?subject=subscribe>
X-List-Received-Date: Thu, 23 Feb 2023 14:18:42 -0000
Signed-off-by: Christoph Heiss <c.heiss@proxmox.com>
---
Changes v1 -> v2:
* Incorporate suggestions made by Thomas
qm.adoc | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/qm.adoc b/qm.adoc
index 8a49283..93ec29d 100644
--- a/qm.adoc
+++ b/qm.adoc
@@ -1061,6 +1061,28 @@ operations that have the potential to write out zeros to the storage:
On a thin provisioned storage, this can help to free up unused space.
+Filesystem Freeze & Thaw on Backup
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+By default, guest filesystems are synced via the 'fs-freeze' QEMU Guest Agent
+Command when a backup is performed, to provide consistency.
+
+On Windows guests, some applications might handle consistent backups themselves
+by hooking into the Windows VSS (Volume Shadow Copy Service) layer, a
+'fs-freeze' then might interfere with that. For example, it has been observed
+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
+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.
+
+NOTE: Disabling this option can potentially lead to backups with inconsistent
+filesystems and should therefore only be disabled if you know what you are
+doing.
+
Troubleshooting
^^^^^^^^^^^^^^^
--
2.39.1