From: Fiona Ebner <f.ebner@proxmox.com>
To: pve-devel@lists.proxmox.com
Subject: [pve-devel] [PATCH docs] storage: note that qcow2 internal snapshots are inefficient
Date: Fri, 28 Nov 2025 16:56:09 +0100 [thread overview]
Message-ID: <20251128155628.223336-1-f.ebner@proxmox.com> (raw)
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 <f.ebner@proxmox.com>
---
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
--
2.47.3
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