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Il 09/01/2025 12:57, Fabian Grünbichler ha scritto:
Alexandre Derumier via pve-devel <pve-devel@lists.proxmox.com> hat am
16.12.2024 10:12 CET geschrieben:
it would be great if there'd be a summary of the design choices and a high
level summary of what happens to the files and block-node-graph here. it's a
bit hard to judge from the code below whether it would be possible to eliminate
the dynamically named block nodes, for example ;)
a few more comments documenting the behaviour and ideally also some tests
(mocking the QMP interactions?) would be nice
@Alexandre Derumier: Thanks for add external snapshot support, I have
not looked at the implementation in detail because I do not have enough
time but I think external snapshot support would be useful.
I used it outside of proxmox years ago, on Debian servers with VMs
managed with libvirt, I managed external snapshots completely manually
from cli with multiple commands because they were not implemented in
virtmanager and they were useful to save a lot of time (instead of
backup/restore) in some high-risk operations on VMs with large disks,
raw pre-allocated on hdd disks.
I used them very little and kept them only the minimum time necessary
for delicate maintenance operations, if there were unforeseen events it
returned to the situation before the snapshot, I deleted the external
snapshot and created another one to try again, if instead everything was
ok in the end I did the commit, and went back to using only the
pre-allocated raw image. With high disk usage as in the operations I was
doing the performance decrease with external qcow2 snapshots compared to
just pre-allocated raw disks was huge if I remember correctly (which is
why I used them for the minimum amount of time possible).
If it hasn't already been planned I think it could be useful to warn
users (atleast in documentation) to avoid them underestimating their
possible impact on performance (especially if they basically have
pre-allocated raw on hdd disks for greater performance and minimal
defragmentation) and avoid use or keep them for a long time without real
need. Another important thing to notify users is the increase in space
usage (again mainly for those who are used to pre-allocated disks where
they usually don't risk increases in space).
In this implementation I don't see the possibility of using them on raw
disks (on files) from a fast look, or am I wrong? If so, why? I think
the main use would be in cases like that where you don't have snapshot
support by default
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