The migrate-setmaxdowntime command sets the max allowed downtime during
live-migration, but since `snapshot-create` performs qmp migration, it also
affects the downtime during internal/external snapshot creation.

Resolves: https://gitlab.com/libvirt/libvirt/-/issues/593
Signed-off-by: Abhiram Tilak <atp.exp@gmail.com>
---
This issue was a minor change, yet it has remained without any updates for
some time.

 docs/manpages/virsh.rst | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/docs/manpages/virsh.rst b/docs/manpages/virsh.rst
index fa038e4547..18bdae53c9 100644
--- a/docs/manpages/virsh.rst
+++ b/docs/manpages/virsh.rst
@@ -3717,7 +3717,8 @@ migrate-setmaxdowntime

 Set maximum tolerable downtime for a domain which is being live-migrated to
 another host.  The *downtime* is a number of milliseconds the guest is allowed
-to be down at the end of live migration.
+to be down at the end of live migration. This is also used to set the max
+downtime for creating a snapshot using ``snapshot-create``.


 migrate-setspeed
--
2.44.0
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On Mon, May 13, 2024 at 01:36:27 +0530, Abhiram Tilak wrote:
> The migrate-setmaxdowntime command sets the max allowed downtime during
> live-migration, but since `snapshot-create` performs qmp migration, it also
> affects the downtime during internal/external snapshot creation.
> 
> Resolves: https://gitlab.com/libvirt/libvirt/-/issues/593
> Signed-off-by: Abhiram Tilak <atp.exp@gmail.com>
> ---
> This issue was a minor change, yet it has remained without any updates for
> some time.
> 
>  docs/manpages/virsh.rst | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/docs/manpages/virsh.rst b/docs/manpages/virsh.rst
> index fa038e4547..18bdae53c9 100644
> --- a/docs/manpages/virsh.rst
> +++ b/docs/manpages/virsh.rst
> @@ -3717,7 +3717,8 @@ migrate-setmaxdowntime
> 
>  Set maximum tolerable downtime for a domain which is being live-migrated to
>  another host.  The *downtime* is a number of milliseconds the guest is allowed
> -to be down at the end of live migration.
> +to be down at the end of live migration. This is also used to set the max
> +downtime for creating a snapshot using ``snapshot-create``.

While this is true, the usefulness of setting max downtime for snapshots
is questionable at best. Snapshots are mostly created in paused state
when this doesn't make sense at all since the VM is "down" the whole
time.

During "live" snapshots (which are not used very much as the memory
image will be unnecessarily large) this might apply, but generally local
storage is usually fast enough for this to not be a problem.

I'm not sure what this bit of documentation would provide to the user.
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On Mon, 13 May 2024 at 13:38, Peter Krempa <pkrempa@redhat.com> wrote:

> On Mon, May 13, 2024 at 01:36:27 +0530, Abhiram Tilak wrote:
> > The migrate-setmaxdowntime command sets the max allowed downtime during
> > live-migration, but since `snapshot-create` performs qmp migration, it
> also
> > affects the downtime during internal/external snapshot creation.
> >
> > Resolves: https://gitlab.com/libvirt/libvirt/-/issues/593
> > Signed-off-by: Abhiram Tilak <atp.exp@gmail.com>
> > ---
> > This issue was a minor change, yet it has remained without any updates
> for
> > some time.
> >
> >  docs/manpages/virsh.rst | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/docs/manpages/virsh.rst b/docs/manpages/virsh.rst
> > index fa038e4547..18bdae53c9 100644
> > --- a/docs/manpages/virsh.rst
> > +++ b/docs/manpages/virsh.rst
> > @@ -3717,7 +3717,8 @@ migrate-setmaxdowntime
> >
> >  Set maximum tolerable downtime for a domain which is being
> live-migrated to
> >  another host.  The *downtime* is a number of milliseconds the guest is
> allowed
> > -to be down at the end of live migration.
> > +to be down at the end of live migration. This is also used to set the
> max
> > +downtime for creating a snapshot using ``snapshot-create``.
>
> While this is true, the usefulness of setting max downtime for snapshots
> is questionable at best. Snapshots are mostly created in paused state
> when this doesn't make sense at all since the VM is "down" the whole
> time.
>
> During "live" snapshots (which are not used very much as the memory
> image will be unnecessarily large) this might apply, but generally local
> storage is usually fast enough for this to not be a problem.
>
> I'm not sure what this bit of documentation would provide to the user.
>
>
Yeah, I also think it makes more sense to mention how the flag affects
snapshot-create
in the snapshot-create documentation, especially where we talk about taking
live
snapshots, instead of doing so under migrate-setdowntimemax's. Otherwise,
this
this doesn't look quite helpful. --
Abhiram
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