From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from firstgate.proxmox.com (firstgate.proxmox.com [IPv6:2a01:7e0:0:424::9]) by lore.proxmox.com (Postfix) with ESMTPS id 77DA61FF136 for ; Mon, 23 Mar 2026 12:06:31 +0100 (CET) Received: from firstgate.proxmox.com (localhost [127.0.0.1]) by firstgate.proxmox.com (Proxmox) with ESMTP id 7933112993; Mon, 23 Mar 2026 12:06:48 +0100 (CET) From: Fiona Ebner To: pve-devel@lists.proxmox.com Subject: [PATCH v2 docs] storage: note that qcow2 internal snapshots are inefficient Date: Mon, 23 Mar 2026 12:06:25 +0100 Message-ID: <20260323110642.51984-1-f.ebner@proxmox.com> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Bm-Milter-Handled: 55990f41-d878-4baa-be0a-ee34c49e34d2 X-Bm-Transport-Timestamp: 1774263959331 X-SPAM-LEVEL: Spam detection results: 0 AWL 0.003 Adjusted score from AWL reputation of From: address BAYES_00 -1.9 Bayes spam probability is 0 to 1% DMARC_MISSING 0.1 Missing DMARC policy KAM_DMARC_STATUS 0.01 Test Rule for DKIM or SPF Failure with Strict Alignment RCVD_IN_VALIDITY_CERTIFIED_BLOCKED 0.001 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. RCVD_IN_VALIDITY_RPBL_BLOCKED 0.001 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. RCVD_IN_VALIDITY_SAFE_BLOCKED 0.001 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record SPF_PASS -0.001 SPF: sender matches SPF record Message-ID-Hash: VCXLYGW6DZE7GVQ57N7GBANEZ32V25NP X-Message-ID-Hash: VCXLYGW6DZE7GVQ57N7GBANEZ32V25NP X-MailFrom: f.ebner@proxmox.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; loop; banned-address; emergency; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header X-Mailman-Version: 3.3.10 Precedence: list List-Id: Proxmox VE development discussion List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: It's a commonly reported issue, often also in the enterprise support, that taking or removing snapshots of large qcow2 files on file-based network storages can take a very long time. Add a note about this limitation. Signed-off-by: Fiona Ebner --- Changes in v2: * add recommendation about doing the operations offline pvesm.adoc | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/pvesm.adoc b/pvesm.adoc index c634f6b..97feca0 100644 --- a/pvesm.adoc +++ b/pvesm.adoc @@ -88,6 +88,12 @@ block device functionality. ^2^: On file based storages, snapshots are possible with the 'qcow2' format, either using the internal snapshot function, or snapshots as volume chains^4^. +Creating and deleting internal 'qcow2' snapshots will block a running VM and +is not an efficient operation. The performance is particularly bad with network +storages like NFS. On some setups and for large disks (multiple hundred GiB or +TiB sized), these operations may take several minutes, or in extreme cases, even +hours. If your setup is affected, create and remove snapshots while the VM is +shut down, expecting a long task duration. ^3^: It is possible to use LVM on top of an iSCSI or FC-based storage. That way you get a `shared` LVM storage -- 2.47.3