On Thu, May 4, 2017 at 11:09 PM Michal Skrivanek <michal.skrivanek@redhat.com> wrote:

> On 4 May 2017, at 17:51, Gianluca Cecchi <gianluca.cecchi@gmail.com> wrote:
>
> Hello,
> supposing to have a Linux VM with ovirt-guest-agent installed,

File system freezing is implemented using libvirt fsFreese/fsThaw, and is

implemented in the guest with qemu-guest-agent, not ovirt-guest-agent.

You can find the info on using it here:

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Virtualization_Deployment_and_Administration_Guide/sect-Using_the_QEMU_guest_virtual_machine_agent_protocol_CLI-libvirt_commands.html

during a live snapshot operation it should be freeze of filesystems.
> Where to find confirmation of correct/successful interaction?

if it’s not successful there should be an event log message about that. And prior to taking the snapshot a warning in red at the bottom of the dialog (that check happens when you open the dialog, so it may not be 100% reliable)

> /var/log/messages or agent log or other kind of files?

if you want to doublecheck then this is noticable in vdsm.log. First we try to take the snapshot with fsfreeze, and only when it fails we take it again without it.

Since 3.6 we use fsFreeze/fsThaw explicitly, so we don't try snapshot twice.

In vdsm log you will find an INFO log before/after fsFreeze/fsThaw, or WARN log if they failed.

> Are there any limitations on filesystems that support freeze? Is it fsfreeze the command executed at VM OS level or any other low level command?

It’s a matter of Linux and Windows implementation, they both have an API supporting that at kernel level. I’m not aware of filesystem limitations.

You should check qemu-guest-agent documentation.

Nir