[ovirt-users] ovirt upgrade => vms refusing to (re)boot

[Nelson Lameiras]

Hello, 

We had a rather unpleseant surprise while upgrading our production datacenters to oVirt 4.0 => 4.1 (although I think this problem is not related to oVirt 4.1). 
Some critical VMs simply refused to reboot without any particular error message other than "VM failed to boot" 

After a stressfull 2h of investigation, it turns out that the problematic VMs shared the same "exotic" condition. They were not rebooted since the latest major upgrade 3.6 => 4.0 (I know, this is not a good practise and we underestimated it's priority, we will change our reboot policies) 
Their "custom compatilibity setting" was set to 3.6 !! When changing this setting to "Empty", The VM booted normaly. Hard to find, easy to fix !! ;) 

Neverthess, there is little to none information/documentation about the usefullness of this setting, and I have a hard time understanding the consequences of changing it manually. 

Our oVirt datacenter (which has engine 4.1.1, but some hosts on 4.0, so it's still on 4.0 compatibility) hosts currently +- 200 Vms, 
- 10 with "custom compatilibity setting" set to 3.6 - which will not (reb)boot in current state, 
- 30some with "custom compatilibity setting" set to 4.0 - which (re)boot normally 
- the rest with "custom compatilibity setting" set to "empty" - which (re)boot normally 

So can a oVirt guru please answer the following questions : 

- What does this setting do? which are the consequences of changing it manually ? 
- Is it "normal" that a VM not reboooted since the 3.6 update does not boot if a new major upgrade is done on hostig host ? (maybe a exotic bug worth correcting ?) 
- Which are the possible consequences of manually setting this setting to "Empty" in all my VMs (running or stopped) ? 
- Which events will change this setting automatically ? (cluster major version upgrade, first reboot after upgrade, ...) ? 
- Some of my VMs have custom_compatibility_version set to 4.0 (in REST API) eventough they have been recently rebooted and "custom compatilibity setting" is empty in GUI, who's this possible ? 

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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