[ovirt-users] vhostmd vdsm-hook

[Simon Barrett]

Thanks again but how does that work when a VM is configured to have more than one disk?

If I have a VM with a /dev/vda disk and a /dev/vdb disk, when I turn the vhostmd hook on the vm metric device gets created  as /dev/vdb and the original /dev/vdb disk gets bumped to /dev/vdc.

Is that expected behavior? Will that not cause problems?

Thanks,

Simon

From: Arsène Gschwind [mailto:arsene.gschwind at unibas.ch]
Sent: Tuesday, 19 April, 2016 13:06
To: Simon Barrett <Simon.Barrett at tradingscreen.com>; users at ovirt.org
Subject: Re: [ovirt-users] vhostmd vdsm-hook

The metric information are available on this additional disk /dev/vdb. You may install the package vm-dump-metrics and use the command vm-dump-metrics which will display all metrics in an xml format.

Arsène
On 04/19/2016 10:48 AM, Simon Barrett wrote:
Thanks Arsène,

I have vhostmd running on the ovirt node and have set the sap_agent to true on the VM configuration. I also stopped and started the VM to ensure that the config change took effect.

On the oVirt node I see the vhostmd running and see the following entry in the qemu-kvm output:

drive file=/dev/shm/vhostmd0,if=none,id=drive-virtio-disk701,readonly=on,format=raw -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x8,drive=drive-virtio-disk701,id=virtio-disk701

The part I wasn't quite understanding was how this presented itself on the VM but I now see a new disk device "/dev/vdb". If I cat the contents of /dev/vdb I now see the information that is provided from the ovirt node, which is great news and very useful.

Thanks for your help.

Simon

From: users-bounces at ovirt.org<mailto:users-bounces at ovirt.org> [mailto:users-bounces at ovirt.org] On Behalf Of Arsène Gschwind
Sent: Monday, 18 April, 2016 16:03
To: users at ovirt.org<mailto:users at ovirt.org>
Subject: Re: [ovirt-users] vhostmd vdsm-hook

Hi Simon,

You will need to have vhostmd running on the oVirt node and set the "sap_agent" custom property for the vm as you may see on the screenshot.

[sap_agent]

Arsène
On 04/15/2016 12:15 PM, Simon Barrett wrote:
I'm trying to use the vhostmd vdsm host to access ovirt node metrics from within a VM. Vhostmd is running and updating the /dev/shm/vhostmd0 on the ovirt node.

The part I'm stuck on is: "This disk image is exported read-only to guests. Guests can read the disk image to see metrics" from http://www.ovirt.org/develop/developer-guide/vdsm/hook/vhostmd/

Does the hook do this by default? I don't see any new read-only device mounted in the guest. Is there additional work I need to do to mount this and access the data from within the guest?

Many thanks,

Simon





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