[pve-devel] [RFC qemu/guest-common/manager/qemu-server/docs 00/13] fix #4136: implement backup fleecing
Roland Kletzing
devzero at web.de
Thu Jan 25 17:39:37 CET 2024
yes, fantastic news, i did not reckon that we have progress here that
soon! :)
thanks very much for this effort, this is a great step forward!
roland
Am 25.01.24 um 17:02 schrieb DERUMIER, Alexandre:
> oh!!! Thanks you very much Fiona !!!
>
> This is really the blocking feature for me, still not using pbs because
> of this.
>
> I'll try to build a lab for testing as soon as possible
> (I'm a bit busy with fosdem preparation)
>
> I'l also to test vm crash/host crash when backup is running, to see
> how it's handled.
>
>
> -------- Message initial --------
> De: Fiona Ebner <f.ebner at proxmox.com>
> Répondre à: Proxmox VE development discussion <pve-
> devel at lists.proxmox.com>
> À: pve-devel at lists.proxmox.com
> Objet: [pve-devel] [RFC qemu/guest-common/manager/qemu-server/docs
> 00/13] fix #4136: implement backup fleecing
> Date: 25/01/2024 15:41:36
>
> When a backup for a VM is started, QEMU will install a
> "copy-before-write" filter in its block layer. This filter ensures
> that upon new guest writes, old data still needed for the backup is
> sent to the backup target first. The guest write blocks until this
> operation is finished so guest IO to not-yet-backed-up sectors will be
> limited by the speed of the backup target.
>
> With backup fleecing, such old data is cached in a fleecing image
> rather than sent directly to the backup target. This can help guest IO
> performance and even prevent hangs in certain scenarios, at the cost
> of requiring more storage space.
>
> With this series it will be possible to enable backup-fleecing via
> e.g. `vzdump 123 --fleecing enabled=1,storage=local-zfs` with fleecing
> images created on the storage `local-zfs`. If no storage is specified,
> the fleecing image will be created on the same storage as the original
> image.
>
>
> Fleecing images are created by qemu-server via pve-storage and
> attached to QEMU before the backup starts, and cleaned up after the
> backup finished or failed. Currently, just a "-fleecing(.raw)" suffix
> is added and there is no special handling yet for e.g. qm rescan/etc..
> And previous left-overs are not automatically cleaned up, because
> while unlikely, images with this name might've been created by a user
> too. Happy to discuss alternatives!
>
> The fleecing image needs to be the exact same size as the source, but
> luckily, an explicit size can be specified when attaching a raw image
> to QEMU so there are no size issues when using storages that have
> coarser allocation/round up.
>
>
> While initial tests seem fine, bitmap handling needs to be carefully
> checked for correctness. More eyeballs can't hurt there.
>
> QEMU patches are for the submodule for better reviewability. There are
> unfortunately a few prerequisites which are also still being worked on
> upstream. These are:
>
> Fix for qcow2 block status querying when used as a source image [0].
> Already reviewed and being pulled.
>
> For being able to discard the fleecing image, addition of a
> discard-source parameter[1]. This series was adapted for downstream
> and I tried to address the two remaining issues:
>
> 1. Permission issue when backup source node is read-only (e.g. TMP
> state): Made permissions conditional for when discard-source is set
> with a new option for the copy-before-write block driver. Currently,
> it's part of QAPI, nicer would be to make it internal-only.
>
> 2. Cluster size issue when fleecing image has a larger cluster size
> than backup target: Made a workaround by also considering source image
> when calculating cluster size for block copy and had to hack
> .bdrv_co_get_info implementations for snapshot-access and
> copy-before-write. Not super confident and better to wait for an
> answer from upstream.
>
> Upstream reports/discussions for these can also be found at [1].
>
>
> No hard dependencies AFAICS, but of course pve-manager should depend
> on both new pve-guest-common and qemu-server to actually be able to
> use the option.
>
>
> [0]:
> https://antiphishing.vadesecure.com/v4?f=SVN0TjFBb1k5Qk8zQ2E1YTzVLi48fY
> wOWQgYFfxt7g0KvdT5nea3YyBhm5UJw1fuk8HWaPXl-
> BfpYUXNTonGgg&i=YXJwbnI5ZGY3YXM2MThBYezeqTiyfur56l5--
> I5CLrY&k=ogd1&r=d2RpVFJVaTVtcFJRWFNMYgYCddP93Y9SOEaGwAD-
> 9JdLrx2JwwKfs9Sn_uiRQCCUgqnCg4WLD-
> gLY0eKXrXX4A&s=d8690db845451bca9cb2f13496bf1af08b8e72a9fa856ee81c1ca437
> cd57b2cb&u=https%3A%2F%2Flore.kernel.org%2Fqemu-
> devel%2F20240116154839.401030-1-f.ebner%40proxmox.com%2F
> [1]:
> https://antiphishing.vadesecure.com/v4?f=SVN0TjFBb1k5Qk8zQ2E1YTzVLi48fY
> wOWQgYFfxt7g0KvdT5nea3YyBhm5UJw1fuk8HWaPXl-
> BfpYUXNTonGgg&i=YXJwbnI5ZGY3YXM2MThBYezeqTiyfur56l5--
> I5CLrY&k=ogd1&r=d2RpVFJVaTVtcFJRWFNMYgYCddP93Y9SOEaGwAD-
> 9JdLrx2JwwKfs9Sn_uiRQCCUgqnCg4WLD-
> gLY0eKXrXX4A&s=4f49e8ee5b68a6da0c3835c1aebb78501573f9d4f88a503b0c56859a
> 3afa6e2f&u=https%3A%2F%2Flore.kernel.org%2Fqemu-
> devel%2F20240117160737.1057513-1-vsementsov%40yandex-team.ru%2F
>
> qemu:
>
> Fiona Ebner (6):
> backup: factor out gathering device info into helper
> backup: get device info: code cleanup
> block/io: clear BDRV_BLOCK_RECURSE flag after recursing in
> bdrv_co_block_status
> block/{copy-before-write,snapshot-access}: implement bdrv_co_get_info
> driver callback
> block/block-copy: always consider source cluster size too
> PVE backup: add fleecing option
>
> Vladimir Sementsov-Ogievskiy (2):
> block/copy-before-write: create block_copy bitmap in filter node
> qapi: blockdev-backup: add discard-source parameter
>
> block/backup.c | 15 +-
> block/block-copy.c | 36 ++--
> block/copy-before-write.c | 46 ++++-
> block/copy-before-write.h | 1 +
> block/io.c | 10 ++
> block/monitor/block-hmp-cmds.c | 1 +
> block/replication.c | 4 +-
> block/snapshot-access.c | 7 +
> blockdev.c | 2 +-
> include/block/block-copy.h | 3 +-
> include/block/block_int-global-state.h | 2 +-
> pve-backup.c | 234 +++++++++++++++++++------
> qapi/block-core.json | 18 +-
> 13 files changed, 300 insertions(+), 79 deletions(-)
>
>
> guest-common:
>
> Fiona Ebner (1):
> vzdump: schema: add fleecing property string
>
> src/PVE/VZDump/Common.pm | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
>
> manager:
>
> Fiona Ebner (1):
> vzdump: handle new 'fleecing' property string
>
> PVE/VZDump.pm | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
>
> qemu-server:
>
> Fiona Ebner (2):
> backup: disk info: also keep track of size
> backup: implement fleecing option
>
> PVE/VZDump/QemuServer.pm | 141 ++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 139 insertions(+), 2 deletions(-)
>
>
> docs:
>
> Fiona Ebner (1):
> vzdump: add section about backup fleecing
>
> vzdump.adoc | 28 ++++++++++++++++++++++++++++
> 1 file changed, 28 insertions(+)
>
>
> Summary over all repositories:
> 17 files changed, 504 insertions(+), 0 deletions(-)
>
>
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