VDSM has the following config option:

# Maximum concurrent outgoing migrations
# max_outgoing_migrations = 2

On Tue, 2017-04-18 at 18:48 +0200, Nelson Lameiras wrote:
hello,

When putting a host on "maintenance mode", all vms start migrating to other 
hosts.

We have some hosts that have 60 vms. So this will create a 60 vms migrating 
simultaneously.
Some vms are under so much heavy loads that migration fails often (our guess is 
that massive simultaneous migrations does not help migration convergence) - 
even with "suspend workload if needed" migraton policy.

- Does oVirt really launches 60 simultaneous migrations or is there a queuing 
system ?
- If there is a queuing system, is there a way to configure a maximum number of 
simultaneous migrations ?

I did see a "migration bandwidth limit", but this is quite what we are looking 
for.

my setup:
ovirt-engine +hosted engine 4.1.1
hosts : centos 7.3 fully updated.

for full context to understand this question : 2 times in the past, when trying 
to put a host in maintenance, host stopped responding during massive migrations 
and was fenced by engine. It's still unclear why host stopped responding, but 
we think that migrating 60+ vms simultaneously puts a heavy strain on storage ? 
So we would like to better control migration process in order to better 
understand what's happening. This scenario is "production only" since our labs 
do not contain nearly as much vm with such heavy loads. So rather than trying 
to reproduce, we are trying to avoid ;)

cordialement, regards,

[cid:1492535709.17056.4.camel@acronis.com]<https://www.lyra-network.com/>

Nelson LAMEIRAS
Ingénieur Systèmes et Réseaux / Systems and Networks engineer
Tel: +33 5 32 09 09 70
nelson.lamei...@lyra-network.com<mailto:nelson.lamei...@lyra-network.com>

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