[PATCH SERIES v2 pve-storage/qemu-server] add external qcow2 snapshot support

[Alexandre Derumier]

This patch series implement qcow2 external snapshot support for files && lvm volumes

The current internal qcow2 snapshots have a lot of performance problems.

I have tested through nfs and also local filesystem
https://lore.proxmox.com/pve-devel/6a44716a-88bc-4523-b210-d67031917d8f@proxmox.com/t/

I see that Fiona don't have same result than me, but I got something like 200~300iops
vs 20000 iops with 4k randwrite when a snapshot exist.

The result is even worst on a shared filesystem like ocfs2 or gfs2. (around 80 iops)
I think (I'm not 100% sure) this is mostly because metadatas are not preallocated
anymore with qcow2 internal snap.

With external snapshot, I almost don't have any performance impact when a snapshot exist.

Also other bugs are freeze/lock reported by users since years on snapshots delete on nfs
https://forum.proxmox.com/threads/snapshot-removal-jams-the-vm.111648/
(The disk access seem to be frozen during all the delete duration)

External qcow2 snapshots also allow snapshot of raw devices ,so 0 performance impact without snapshots.

This also open doors for remote snapshot export-import for storage replication.

This V2 introduce support for qcow2 external snapshot for lvm, extra lvm
volume is created for each snapsphot and formated with qcow2.
This is a lot more performant than lvm (non-thin/nomedata) snapshot, and allow to use
it for shared lvm.  (I have another patch series for thick lvm dynamic extend, but if we could have at minimum
snapshot working, it could great :)

I have tested: snasphot, snap rollback, snap delete, clone, move disk, rename disk, create_base. (online && offline)

lxc is not yet supported, but I think we could look to implement the recent dm-qcow2 kernel block driver
https://lore.kernel.org/lkml/164846619932.251310.3668540533992131988.stgit@pro/T/


storage.cfg example:

dir: local2
        path /var/liv/vz
        content snippets,vztmpl,backup,images,iso,rootdir
        snapext 1

lvmqcow2:test
        vgname test
        snapext 1
        content images


changelog v2:
 implement lvm with external qcow2 snapshots

pve-storage:

Alexandre Derumier (2):
  add external snasphot support
  add lvmqcow2 plugin: (lvm with external qcow2 snapshot)

 src/PVE/Storage.pm                |   2 +
 src/PVE/Storage/DirPlugin.pm      |   1 +
 src/PVE/Storage/LvmQcow2Plugin.pm | 460 ++++++++++++++++++++++++++++++
 src/PVE/Storage/Makefile          |   3 +-
 src/PVE/Storage/Plugin.pm         | 225 +++++++++++++--
 5 files changed, 665 insertions(+), 26 deletions(-)
 create mode 100644 src/PVE/Storage/LvmQcow2Plugin.pm


qemu-server:


Alexandre Derumier (1):
  implement external snapshot

 PVE/QemuServer.pm | 108 ++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 95 insertions(+), 13 deletions(-)

-- 
2.39.2