From 95871caa2911a0cb86967fd0c0c67a3c38757653 Mon Sep 17 00:00:00 2001 From: Thomas Lamprecht Date: Fri, 18 Jul 2025 08:44:23 +0200 Subject: [PATCH] lvm storage: improve wording for snapshot-as-volume-chain option Suggested-by: Friedrich Weber Signed-off-by: Thomas Lamprecht --- pve-storage-lvm.adoc | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/pve-storage-lvm.adoc b/pve-storage-lvm.adoc index 31964c7..422833d 100644 --- a/pve-storage-lvm.adoc +++ b/pve-storage-lvm.adoc @@ -51,8 +51,13 @@ Wipe throughput (`cstream -t` parameter value). `snapshot-as-volume-chain`:: Set this flag to enable snapshot support for virtual machines on LVM with a -volume backing chain that uses separate volumes for snapshot virtual disk -states. +volume backing chain. +With this setting, taking a snapshot persists the current virtual disk state to +a separate volume. A volume based on a snapshot references its parent snapshot +volume as its backing volume and records only the differences to that backing +volume. +Snapshot volumes are currently thick-provisioned LVM logical volumes, but the +underlying block storage may provide thin provisioning. + This design avoids issues with native LVM snapshots, such as significant input/output (I/O) penalties and unexpected, dangerous behavior when running out @@ -63,8 +68,9 @@ storage system that supports block storage. This includes iSCSI and fiber channel-attached SANs. + Note that, although this feature relies on qcow2, it only uses qcow2's ability -to layer multiple volumes in a backing chain. The snapshot functionality itself -is managed by the PVE storage system, not qcow2 directly. +to layer multiple volumes in a backing chain, not qcow2's snapshot +functionality. +The snapshot functionality is managed by the PVE storage system. + Enabling or disabling this flag only affects newly created virtual disk volumes.