On Thu, Mar 9, 2017 at 12:11 PM, Maton, Brett <matonb@ltresources.co.uk> wrote:

Good point

Just wanted to add that freezing activity is not only important for
databases, but also for plain file systems. In order to do a consistent
backup it is important to freeze the file systems before creating a live
snapshot, and thaw it afterwards. oVirt does that automatically, but
only if the guest agent is installed and running. So, remember to have
the guest agent installed and running in the virtual machines that you
plan to backup using this mechanism.

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Yes, indeed.

I forgot to write it before, but I did verify that my VM with guest agent installed had this inside its /var/log/messages file:

Mar 9 10:49:36 T-ORACLE73 qemu-ga: info: guest-fsfreeze called

Mar 9 10:49:36 T-ORACLE73 qemu-ga: info: executing fsfreeze hook with arg 'freeze'

Mar 9 10:49:37 T-ORACLE73 qemu-ga: info: executing fsfreeze hook with arg 'thaw'

Also, with vm_backup.py utility, I verified that inside the VM where the snapshotted disk was attached (c7testovn1), I got this:

Mar 9 10:49:42 c7testovn1 kernel: pci 0000:00:09.0: BAR 4: assigned [mem 0x40000000-0x40003fff 64bit pref]

Mar 9 10:49:42 c7testovn1 kernel: pci 0000:00:09.0: BAR 1: assigned [mem 0x40004000-0x40004fff]

Mar 9 10:49:42 c7testovn1 kernel: pci 0000:00:09.0: BAR 0: assigned [io 0x1000-0x103f]

Mar 9 10:49:42 c7testovn1 kernel: virtio-pci 0000:00:09.0: enabling device (0000 -> 0003)

Mar 9 10:49:42 c7testovn1 kernel: vdb: vdb1 vdb2

Mar 9 10:49:42 c7testovn1 systemd: Starting LVM2 PV scan on device 252:18...

Mar 9 10:49:42 c7testovn1 lvm: 2 logical volume(s) in volume group "mainvg" now active

Mar 9 10:49:42 c7testovn1 systemd: Started LVM2 PV scan on device 252:18.

Mar 9 10:49:44 c7testovn1 systemd: Stopping LVM2 PV scan on device 252:18...

Mar 9 10:49:44 c7testovn1 lvm: Device 252:18 not found. Cleared from lvmetad cache.

Mar 9 10:49:44 c7testovn1 systemd: Stopped LVM2 PV scan on device 252:18.

Gianluca