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Hi,
It's clear now :) My current implementation allows only for group
snapshots if the storage supports it, and regular sequential snapshots
otherwise. Due to the considerations around
application/crash-consistency, it would be best to let the user pick
(with a default set by the storage plugin/backend?).
On 21/11/2024 16:49, Max Carrara wrote:
On Wed Nov 20, 2024 at 5:10 PM CET, Ivaylo Markov wrote:
Hello,
I've been caught up in other things and it's been a while, but as I was
collating and testing my proposed changes, I came across this again and
thought I'd clarify something.
On 08/10/2024 13:50, Max Carrara wrote:
I was directed here to discuss this proposal and my implementation idea
after an initial post in Bugzilla[1]. The goal is to give storage
plugins the option to perform atomic crash-consistent snapshots of the
virtual disks associated with a virtual machine where the backend
supports it (e.g. Ceph, StorPool, and ZFS) without affecting those
without such a feature.
Since you mentioned that the backends without such a feature won't be
affected, will the disks of the storage types that *do* support it still
be addressable individually? As in: Would it be possible to run both
group snapshots and individual snapshots on a VM's disks? (I'm assuming
that they will, but still wanted to ask.)
Do you mean this this as "you can snapshot the whole VM (all disks) at
once *or* each disk individually" or "when making a snapshot of the
entire VM, the user can chose between individual/group snapshot of all
drives". What I have so far matches the first description, but I just
realized you might have meant the second one, so I thought I'd ask and
potentially create more work for myself :)
Hey!
No worries, always feel free to ask :)
I should have phrased myself better there, so I'll try to be as specific
as possible here. Let me define some terms first:
- regular snapshots: This is how things work currently; a snapshot of
each disk of the VM is made after the previous one finishes. In other
words, disk snapshots are made *sequentially*. Works for every storage
type.
- group snapshots: What you're implementing -- essentially creating a
snapshot of *all* disks of a VM at once, atomically. Snapshots of this
type are crash-consistent. Only works for storage types that support
it.
What I meant to ask was whether *both* options will remain available to
users. For example, if I click on a VM, then go to Snapshots -> Take
Snapshot, will I have the option to say whether the snapshot should be a
group snapshot or a regular snapshot?
I guess calling it "individual" was a bit ambiguous here; I didn't mean
that I could e.g. snapshot just one disk only (if that's what confused
you). When performing a snapshot of a VM, a snapshot for *all* disks of
the VM is *always* made, regardless of whether a regular snapshot or a
group snapshot is performed on a VM.
I hope all that isn't too long -- just wanted to make sure everything's
clear! :)
--
Ivaylo Markov
Quality & Automation Engineer
StorPool Storage
https://www.storpool.com
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