[ovirt-users] trouble when creating VM snapshots including memory

[Matthias Leopold]

hi,

i'm having trouble creating VM snapshots that include memory in my oVirt 
4.1 test environment. when i do this the VM gets paused and shortly 
(20-30s) afterwards i'm seeing messages in engine.log about both iSCSI 
storage domains (master storage domain and data storage where VM 
resides) experiencing high latency. this quickly worsens from the 
engines view: VM is unresponsive, Host is unresponsive, engine wants to 
fence the host (impossible because it's the only host in the test 
cluster). in the end there is an EngineException

EngineException: 
org.ovirt.engine.core.vdsbroker.vdsbroker.VDSNetworkException: 
VDSGenericException: VDSNetworkException: Message timeout which can be 
caused by communication issues (Failed with error VDS_NETWORK_ERROR and 
code 5022)

the snapshot fails and is left in an inconsistent state. the situation 
has to be resolved manually with unlock_entity.sh and maybe lvm 
commands. this happened twice in exactly the same manner. VM snapshots 
without memory for this VM are not a problem.

VM guest OS is CentOS7 installed from one of the ovirt-image-repository 
images. it has the oVirt guest agent running.

what could be wrong?

this is a test environment where lots of parameters aren't optimal but i 
never had problems like this before, nothing concerning network latency. 
iSCSI is on a FreeNAS box. CPU, RAM, ethernet (10GBit for storage) on 
all hosts involved (engine hosted externally, oVirt Node, storage) 
should be OK by far.

it looks like some obvious configuration botch or performance bottleneck 
to me. can it be linked to the network roles (management and migration 
network are on a 1 GBit link)?

i'm still new to this, not a lot of KVM experience, too. maybe someone 
recognizes the culprit...

thx
matthias