On 05/08, Ignazio Cassano wrote:
> Hello, firstly let me to thank you for reply and sorry if I come back to
> ask why when I do the first migration from A to B it takes 20 minutes and
> then, when I migrate from B to A it takes few seconds.
> I wonder if after the first migration memory is reorganized.
> In the first live migration it lost time to get memory pages ?
> Ignazio
>

Hi,

I work on Cinder, so my knowledge on live migrations is mostly limited
to the attach/detach flow of the volumes.

I thought that maybe if you were using ephemeral nova volumes
(non-cinder) maybe the volume had not yet been deleted from the old
node, or maybe it was using a qcow2 base file for multiple instances on
the source (each using a different chain on top of it) and this qcow2
was not originally present in the destination (hence the time to copy
it), so when we do a migration back since there are other instances that
were also using it on the destination (original location) only de
difference needs to be copied.

But these are just brainstorming ideas, since I don't really know how
Nova handles all this.

I would recommend setting Nova log to debug mode in both source and
destination nodes and look at where the time difference really is, in
case it's not where you think it is.

Cheers,
Gorka.


> Il giorno ven 5 ago 2022 alle ore 10:17 Gorka Eguileor <geguileo@redhat.com>
> ha scritto:
>
> > On 04/08, Ignazio Cassano wrote:
> > > HI,
> > > I am using cinder volumes.
> > > Ignazio
> > >
> >
> > Hi,
> >
> > In that case there is no volume data being copied for the instance
> > migration, and volume attach on the destination should not account for
> > more than 30 seconds of those 20 minutes, so not much improvement
> > possible there.
> >
> > Cheers,
> > Gorka.
> >
> > > Il giorno gio 4 ago 2022 alle ore 16:56 Gorka Eguileor <
> > geguileo@redhat.com>
> > > ha scritto:
> > >
> > > > On 03/08, Ignazio Cassano wrote:
> > > > > Hello All,
> > > > > I am looking for a solution to speed up live migration.
> > > > > Instances where ram is used heavily like java application servers,
> > live
> > > > > migration take a long time (more than 20 minutes for 8GB ram
> > instance)
> > > > and
> > > > > converge mode is already set to True in nova.conf.
> > > >
> > > > Hi,
> > > >
> > > > Probably doesn't affect your case, but I assume you are using ephemeral
> > > > nova boot volumes.
> > > >
> > > > Have you tried using only Cinder volumes on the VM?
> > > >
> > > > Cheers,
> > > > Gorka.
> > > >
> > > >
> > > > > I also tried with post_copy but it does not change.
> > > > > After the first live migration (very solow) if I try to migrate
> > again it
> > > > is
> > > > > very fast.
> > > > > I presume the first migration is slow because memory fragmentation
> > when
> > > > an
> > > > > instance is running on the same compute node for a long time.
> > > > > I am looking for a solution considering the on my computing node I
> > can
> > > > have
> > > > > a little ram overcommit. Any case I am increasing the number of
> > compute
> > > > > nodes to reduce it.
> > > > > Thanks
> > > > > Ignazio
> > > >
> > > >
> >
> >