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 B19751FF136 for ; Mon, 23 Mar 2026 11:26:50 +0100 (CET) Received: from firstgate.proxmox.com (localhost [127.0.0.1]) by firstgate.proxmox.com (Proxmox) with ESMTP id 75A7611017; Mon, 23 Mar 2026 11:27:07 +0100 (CET) Message-ID: Date: Mon, 23 Mar 2026 11:27:02 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [pve-devel] [PATCH docs] storage: note that qcow2 internal snapshots are inefficient To: Maximiliano Sandoval References: <20251128155628.223336-1-f.ebner@proxmox.com> Content-Language: en-US From: Fiona Ebner In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Bm-Milter-Handled: 55990f41-d878-4baa-be0a-ee34c49e34d2 X-Bm-Transport-Timestamp: 1774261576825 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: OU5BPUHXBMPUKWIDCWV6VXWZDMFBQBS2 X-Message-ID-Hash: OU5BPUHXBMPUKWIDCWV6VXWZDMFBQBS2 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 CC: pve-devel@lists.proxmox.com X-Mailman-Version: 3.3.10 Precedence: list List-Id: Proxmox VE development discussion List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: Am 23.03.26 um 10:58 AM schrieb Maximiliano Sandoval: > Fiona Ebner writes: >> Am 28.11.25 um 4:56 PM schrieb Fiona Ebner: >>> It's a commonly reported issue, most recently again 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 >>> --- >>> pvesm.adoc | 5 +++++ >>> 1 file changed, 5 insertions(+) >>> >>> diff --git a/pvesm.adoc b/pvesm.adoc >>> index d36baf8..165b446 100644 >>> --- a/pvesm.adoc >>> +++ b/pvesm.adoc >>> @@ -88,6 +88,11 @@ 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. >>> >>> ^3^: It is possible to use LVM on top of an iSCSI or FC-based storage. >>> That way you get a `shared` LVM storage >> >> Ping > > In my experience, users mostly into issues when deleting qcow2 snapshots > on NFS can take up to 10 hours. I would personally put more emphasis on > this specific combination being problematic, and probably mention that > in such case one should delete snapshots while the VM is offline. NFS is already explicitly mentioned as being particularly bad. We also had reports where creating snapshots on NFS took hours. Doing it offline doesn't change the fact that it takes that long, but I guess doing it while offline is still better, because being paused for a long time is not that nice from a guest perspective. I'll add the following in v2: "If your setup is affected, create and remove snapshots while the VM is shut down, expecting a long task duration."