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LVM storage: reword and update to current capabilities

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Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
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Thomas Lamprecht
2025-07-25 11:40:43 +02:00
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pve-storage-lvm.adoc
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@ -8,14 +8,14 @@ endif::wiki[]
Storage pool type: `lvm`
LVM is a light software layer on top of hard disks and partitions. It
can be used to split available disk space into smaller logical
volumes. LVM is widely used on Linux and makes managing hard drives
easier.
LVM is a lightweight software layer that sits on top of hard disks and
partitions. It can be used to divide available disk space into smaller logical
volumes.
Another use case is to put LVM on top of a big iSCSI LUN. That way you
can easily manage space on that iSCSI LUN, which would not be possible
otherwise, because the iSCSI specification does not define a
Another use case is placing LVM on top of a large iSCSI LUN (Logical Unit
Number) or a SAN (Storage Area Network) connected via Fibre Channel.
This allows you to easily manage the space on the iSCSI LUN, which would
otherwise be impossible because the iSCSI specification does not define a
management interface for space allocation.
@ -93,25 +93,31 @@ backend.
Storage Features
~~~~~~~~~~~~~~~~
LVM is a typical block storage, but this backend does not support
snapshots and clones. Unfortunately, normal LVM snapshots are quite
inefficient, because they interfere with all writes on the entire volume
group during snapshot time.
LVM is a typical block storage system.
Unfortunately, regular LVM snapshots are inefficient because they interfere with
all write operations within the entire volume group while the snapshot is
active, which causes significant I/O degradation.
This is why LVM does not support linked clones, and why {pve} added support for
snapshots as volume chains. This feature manages the snapshot volume through the
storage plugin and uses qcow2 to layer separate volumes as a backing chain. This
creates a single disk state that is exposed to the guest.
One big advantage is that you can use it on top of a shared storage,
for example, an iSCSI LUN. The backend itself implements proper cluster-wide
locking.
TIP: The newer LVM-thin backend allows snapshots and clones, but does
not support shared storage.
A benefit of LVM is that it can be used with shared storage.
For example, an iSCSI LUN. The backend implements proper cluster-wide locking if
the storage is marked as shared in the configuration.
TIP: You can use the LVM-thin backend for non-shared local storage. It supports
snapshots and linked clones.
.Storage features for backend `lvm`
[width="100%",cols="m,m,3*d",options="header"]
|==============================================================================
|Content types |Image formats |Shared |Snapshots |Clones
|images rootdir |raw |possible |no |no
|==============================================================================
|===============================================================================
|Content types |Image formats |Shared |Snapshots |Full Clones |Linked Clones
|images rootdir |raw, qcow2 |possible |yes^1^ |yes |no
|===============================================================================
^1^: Since {pve} 9, snapshots as a volume chain have been available for VMs, for
details see the xref:pvesm_lvm_config[LVM configuration] section.
Examples
~~~~~~~~