[pve-devel] [PATCH docs] lvm: add note about requirements of snapshot-as-volume-chains

[pve-devel] [PATCH docs] lvm: add note about requirements of snapshot-as-volume-chains

[Fabian Grünbichler]

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
---

Notes:
    not sure whether we want to also add a note suggesting to (heavily)
    overprovision the LUN/backing device on the storage side, so that there is
    enough "space" for creating snapshots?

 pve-storage-lvm.adoc | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/pve-storage-lvm.adoc b/pve-storage-lvm.adoc
index 6928330..c508fe1 100644
--- a/pve-storage-lvm.adoc
+++ b/pve-storage-lvm.adoc
@@ -57,8 +57,7 @@ snapshot's name and starts a new volume backed by the snapshot.
 +
 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.
+Snapshot volumes are currently thick-provisioned LVM logical volumes.
 +
 This design avoids issues with native LVM snapshots, such as significant
 input/output (I/O) penalties and unexpected, dangerous behavior when running out
@@ -74,6 +73,11 @@ functionality.
 The snapshot functionality is managed by the PVE storage system.
 +
 Enabling or disabling this flag only affects newly created virtual disk volumes.
++
+For efficient support of `snapshot-as-volume-chain`, the backing storage must
+support thin-provisioning and discard. Each snapshot will appear to use the
+full volume size on the PVE side, but the actual space usage on the underlying
+storage will be smaller if those requirements are met.
 
 .Configuration Example (`/etc/pve/storage.cfg`)
 ----
-- 
2.39.5



_______________________________________________
pve-devel mailing list
pve-devel@lists.proxmox.com
https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel

Re: [pve-devel] [PATCH docs] lvm: add note about requirements of snapshot-as-volume-chains

[DERUMIER, Alexandre via pve-devel]

[-- Attachment #1: Type: message/rfc822, Size: 15399 bytes --]

From: "DERUMIER, Alexandre" <alexandre.derumier@groupe-cyllene.com>
To: "pve-devel@lists.proxmox.com" <pve-devel@lists.proxmox.com>
Subject: Re: [pve-devel] [PATCH docs] lvm: add note about requirements of snapshot-as-volume-chains
Date: Sun, 27 Jul 2025 12:03:39 +0000
Message-ID: <d06d26c9f0c5a4c3a23057d2854c76a96714288b.camel@groupe-cyllene.com>

about discard, maybe we should add a note about enabling
issue_discards=1 in lvm.conf. (don't known if it could be enabled by
default for new install ?)


-------- Message initial --------
De: Fabian Grünbichler <f.gruenbichler@proxmox.com>
Répondre à: Proxmox VE development discussion <pve-
devel@lists.proxmox.com>
À: pve-devel@lists.proxmox.com
Objet: [pve-devel] [PATCH docs] lvm: add note about requirements of
snapshot-as-volume-chains
Date: 25/07/2025 11:52:08

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
---

Notes:
    not sure whether we want to also add a note suggesting to (heavily)
    overprovision the LUN/backing device on the storage side, so that
there is
    enough "space" for creating snapshots?

 pve-storage-lvm.adoc | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/pve-storage-lvm.adoc b/pve-storage-lvm.adoc
index 6928330..c508fe1 100644
--- a/pve-storage-lvm.adoc
+++ b/pve-storage-lvm.adoc
@@ -57,8 +57,7 @@ snapshot's name and starts a new volume backed by the
snapshot.
 +
 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.
+Snapshot volumes are currently thick-provisioned LVM logical volumes.
 +
 This design avoids issues with native LVM snapshots, such as
significant
 input/output (I/O) penalties and unexpected, dangerous behavior when
running out
@@ -74,6 +73,11 @@ functionality.
 The snapshot functionality is managed by the PVE storage system.
 +
 Enabling or disabling this flag only affects newly created virtual
disk volumes.
++
+For efficient support of `snapshot-as-volume-chain`, the backing
storage must
+support thin-provisioning and discard. Each snapshot will appear to
use the
+full volume size on the PVE side, but the actual space usage on the
underlying
+storage will be smaller if those requirements are met.
 
 .Configuration Example (`/etc/pve/storage.cfg`)
 ----

[-- Attachment #2: Type: text/plain, Size: 160 bytes --]

_______________________________________________
pve-devel mailing list
pve-devel@lists.proxmox.com
https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel

Re: [pve-devel] [PATCH docs] lvm: add note about requirements of snapshot-as-volume-chains

[Fabian Grünbichler]

On July 27, 2025 2:03 pm, DERUMIER, Alexandre via pve-devel wrote:
> about discard, maybe we should add a note about enabling
> issue_discards=1 in lvm.conf. (don't known if it could be enabled by
> default for new install ?)

yes, maybe. or alternatively, we could call blkdiscard as part of the
removal logic in the storage plugin?


_______________________________________________
pve-devel mailing list
pve-devel@lists.proxmox.com
https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel

[pve-devel] applied: [PATCH docs] lvm: add note about requirements of snapshot-as-volume-chains

[Fiona Ebner]

On Fri, 25 Jul 2025 11:52:08 +0200, Fabian Grünbichler wrote:
> 

Applied, thanks!

[1/1] lvm: add note about requirements of snapshot-as-volume-chains
      commit: a4ad4f48b97cd0334a1d1483815a1c0c4a6fbed3

> not sure whether we want to also add a note suggesting to (heavily)
> overprovision the LUN/backing device on the storage side, so that there is
> enough "space" for creating snapshots?

Would be fine by me, with a warning that space usage needs to be
monitored then.


_______________________________________________
pve-devel mailing list
pve-devel@lists.proxmox.com
https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel

Re: [pve-devel] [PATCH docs] lvm: add note about requirements of snapshot-as-volume-chains

[Friedrich Weber]

On 28/07/2025 10:28, Fabian Grünbichler wrote:
> On July 27, 2025 2:03 pm, DERUMIER, Alexandre via pve-devel wrote:
>> about discard, maybe we should add a note about enabling
>> issue_discards=1 in lvm.conf. (don't known if it could be enabled by
>> default for new install ?)
> 
> yes, maybe. or alternatively, we could call blkdiscard as part of the
> removal logic in the storage plugin?

Just remembered this because it has occasionally come up in enterprise
support that users are confused that deleting LVs doesn't free up space
on (thin-provisioned) LUNs by default. Adding a note about
issue_discards (or, of course, blkdiscard'ing on removal in the storage
plugin) would be nice.


_______________________________________________
pve-devel mailing list
pve-devel@lists.proxmox.com
https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel