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 1DE361FF136 for ; Mon, 23 Mar 2026 13:00:15 +0100 (CET) Received: from firstgate.proxmox.com (localhost [127.0.0.1]) by firstgate.proxmox.com (Proxmox) with ESMTP id 4E61914B6B; Mon, 23 Mar 2026 13:00:32 +0100 (CET) From: Maximiliano Sandoval To: Fiona Ebner Subject: Re: [PATCH v2 docs] storage: note that qcow2 internal snapshots are inefficient In-Reply-To: <20260323110642.51984-1-f.ebner@proxmox.com> (Fiona Ebner's message of "Mon, 23 Mar 2026 12:06:25 +0100") References: <20260323110642.51984-1-f.ebner@proxmox.com> User-Agent: mu4e 1.12.9; emacs 30.1 Date: Mon, 23 Mar 2026 12:59:56 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain X-Bm-Milter-Handled: 55990f41-d878-4baa-be0a-ee34c49e34d2 X-Bm-Transport-Timestamp: 1774267151096 X-SPAM-LEVEL: Spam detection results: 0 AWL 0.126 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: GUMX2YIWG5F6LDODYUYWRA4WMPVGJTHR X-Message-ID-Hash: GUMX2YIWG5F6LDODYUYWRA4WMPVGJTHR X-MailFrom: m.sandoval@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: Fiona Ebner writes: > 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 Looks good to me. Reviewed-by: Maximiliano Sandoval -- Maximiliano