[pve-devel] [PATCH-SERIES v7 pve-storage/qemu-server] add external qcow2 snapshot support

[Fabian Grünbichler]

> Alexandre Derumier via pve-devel <pve-devel at lists.proxmox.com> hat am 04.07.2025 08:44 CEST geschrieben:
> This patch series implement qcow2 external snapshot support for files && lvm volumes
> 
> The current internal qcow2 snapshots have bad write performance because no metadatas can be preallocated.
> 
> This is particulary visible on a shared filesystem like ocfs2 or gfs2.
> 
> Also other bugs are freeze/lock reported by users since years on snapshots delete on nfs
> (The disk access seem to be frozen during all the delete duration)
> 
> This also open doors for remote snapshot export-import for storage replication.

sent some feedback, mostly for the storage and qemu-server <-> storage interface parts,
haven't yet done an in-depth pass over qemu-server or end-to-end.

in particular, the rename_volume vs rename_snapshot and the Plugin snapshot file name/..
questions should probably be solved before the next version 

it would also be great if you could add a patch bumping API version and age and
documenting the changes/new parameters/interfaces - also so that we can ensure
we are on the same page and haven't overlooked anything. AFAICT it should all be
new opt-in or backwards compatible changes, once the feedback is incorporated.

> 
> Changelog v7:
>     - rebased on fiona blockdev work 
> 
> MAIN TODO:
>     - add snapshots tests in both pve-storage && qemu-server
>     - better handle snapshot failure with multiple disks
> 
> pve-storage:
> 
> Alexandre Derumier (10):
>   tests: add lvmplugin test
>   common: add qemu_img_create an preallocation_cmd_option
>   common: qemu_img_create: add backing_file support
>   rename_volume: add source && target snap
>   common: add qemu_img_info helper
>   common: add qemu-img measure
>   storage: volume_snapshot: add $running param
>   qcow2: add external snapshot support
>   lvmplugin: add qcow2 snapshot
>   storage : add volume_support_qemu_snapshot
> 
>  src/PVE/Storage.pm                   |  34 +-
>  src/PVE/Storage/Common.pm            | 116 ++++++
>  src/PVE/Storage/DirPlugin.pm         |  11 +
>  src/PVE/Storage/ESXiPlugin.pm        |   2 +-
>  src/PVE/Storage/ISCSIDirectPlugin.pm |   2 +-
>  src/PVE/Storage/LVMPlugin.pm         | 519 ++++++++++++++++++++----
>  src/PVE/Storage/LvmThinPlugin.pm     |   2 +-
>  src/PVE/Storage/PBSPlugin.pm         |   2 +-
>  src/PVE/Storage/Plugin.pm            | 376 ++++++++++++-----
>  src/PVE/Storage/RBDPlugin.pm         |   8 +-
>  src/PVE/Storage/ZFSPoolPlugin.pm     |   2 +-
>  src/test/Makefile                    |   5 +-
>  src/test/run_test_lvmplugin.pl       | 577 +++++++++++++++++++++++++++
>  13 files changed, 1465 insertions(+), 191 deletions(-)
>  create mode 100755 src/test/run_test_lvmplugin.pl
> 
> qemu-server:
> 
> Alexandre Derumier (3):
>   qemu_img convert : add external snapshot support
>   blockdev: add backing_chain support
>   qcow2: add external snapshot support
> 
>  src/PVE/QemuConfig.pm                         |   4 +-
>  src/PVE/QemuServer.pm                         | 132 +++++--
>  src/PVE/QemuServer/Blockdev.pm                | 345 +++++++++++++++++-
>  src/PVE/QemuServer/QemuImage.pm               |   6 +-
>  src/test/cfg2cmd/simple-backingchain.conf     |  25 ++
>  src/test/cfg2cmd/simple-backingchain.conf.cmd |  33 ++
>  src/test/run_config2command_tests.pl          |  47 +++
>  src/test/run_qemu_img_convert_tests.pl        |  59 +++
>  src/test/snapshot-test.pm                     |   4 +-
>  9 files changed, 620 insertions(+), 35 deletions(-)
>  create mode 100644 src/test/cfg2cmd/simple-backingchain.conf
>  create mode 100644 src/test/cfg2cmd/simple-backingchain.conf.cmd
> 
> -- 
> 2.39.5