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Re: [Qemu-devel] [KVM][Kemari]:Kemari slows down the VM user experience


From: Brian Jackson
Subject: Re: [Qemu-devel] [KVM][Kemari]:Kemari slows down the VM user experience
Date: Tue, 4 Sep 2012 13:14:59 -0500
User-agent: KMail/1.13.7 (Linux/3.2.0-3-amd64; KDE/4.8.4; x86_64; ; )

On Tuesday, September 04, 2012 12:01:31 AM Harshita wrote:
> Hello,
> 
> As part of implementing Fault Tolerant solution, we are exploring
> Kemari. In the process of understanding it, we tested the branch "next"
> of git repository. It is working fine. But, once we trigger sync
> command, VM response is very slow for the actions performed.


That may be why Kemari is basically abandoned. The -next branch hasn't been 
touched in 8 months. The main branch almost 2 years. I think the couple of 
people that were working on it have moved on to other projects.

That said, you didn't mention how your hosts are connected. You need something 
very fast and low latency. Every transaction needs to be replicated and 
ack'ed.


> 
> Observation:
> ------------
> Once sync is started vm is responding slowly. (eg., Mouse operation,
> keys pressed are shown on the screen after some delay.)
> This behavior continues until sync is completed (eg., killing
> guest on the primary or resuming guest on secondary, so that no further
> sync), and then the guest responds normally.
> 
> Our setup:
> ----------
> Host is KVM enabled Linux.
> Tested with both Linux and Windows guests.
> NFS is used to share the disk image.
> 
> Steps followed:
> 1. Start VM on primary(node1)
> qemu-system-x86_64 -hda "/mnt/vm_disks/vm_shared.disk.xm" -m "750"
> -monitor stdio --enable-kvm
> 
> 2. Start VM on secondary(node2), to accept synchronization
> qemu-system-x86_64 -hda "/mnt/vm_disks/vm_shared.disk.xm" -m "750"
> -monitor stdio --enable-kvm -incoming kemari:tcp:0:4444
> 
> 3. Started sync using below command, on primary
> migrate -d kemari:tcp:node2:4444
> 
> 4. 'c' on the virtual terminal of secondary VM to take over completely.
> 
> Can you please let us know if anything missing in the setup or any
> inputs to improve the situation.
> 
> Regards,
> Harshita



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