From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: 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 ; 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 ; 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 ; 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 ; Thu, 23 Feb 2023 15:18:10 +0100 (CET) From: Christoph Heiss 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 List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 23 Feb 2023 14:18:42 -0000 Signed-off-by: Christoph Heiss --- 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