[ovirt-users] massive simultaneous vms migrations ?

Wed Apr 19 09:14:51 UTC 2017

hello pavel, 

Thanks for you answer. 
I did find this parameter (only) in /etc/vdsm/vdsm.conf.rpmnew (??) 

Parameter is commented with value 2 so my guess is that it is not used... So this brings a few more questions : 

- Since parameter is commented, default value must be used... can we be sure that 2 is default value? 
I do found strange that migrations are limited to 2, I have the feeling that more than two are simultaneously being migrated (but I'm maybe wrong), how to be sure? 

cordialement, regards, 

	Nelson LAMEIRAS 
Ingénieur Systèmes et Réseaux / Systems and Networks engineer 
Tel: +33 5 32 09 09 70 
nelson.lameiras at lyra-network.com 

www.lyra-network.com | www.payzen.eu 

Lyra Network, 109 rue de l'innovation, 31670 Labège, FRANCE 

From: "Pavel Gashev" <Pax at acronis.com> 
To: users at ovirt.org, "nelson lameiras" <nelson.lameiras at lyra-network.com> 
Sent: Tuesday, April 18, 2017 7:16:08 PM 
Subject: Re: [ovirt-users] massive simultaneous vms migrations ? 

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, 

	Nelson LAMEIRAS 
	Ingénieur Systèmes et Réseaux / Systems and Networks engineer 
	Tel: +33 5 32 09 09 70 
	nelson.lameiras at lyra-network.com 

	www.lyra-network.com | www.payzen.eu 

Lyra Network, 109 rue de l'innovation, 31670 Labège, FRANCE 

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