Snapshots
---------

There's multiple different ways to create snapshots, the below covers
some basics.

Internal snapshots
~~~~~~~~~~~~~~~~~~

Original and delta are stored in the same QCOW2 file; the disk image
_must_ be QCOW2 format:

- Create an 'internal' snapshot:

    $ virsh snapshot-create-as f24vm snap1 "Clean Fedora-24"

- Revert to a previously known sane state:

    $ virsh snapshot-revert f24vm snap1


External snapshots
------------------

Everytime a snapshot is taken, the current disk becomes a 'backing  le'
& a new QCOW2 overlay is created to track the 'delta'.  (Snapshots are
created instantaneous; excellent for live backups.)

- Create external live disk-only snapshot:

    $ virsh snapshot-create-as \
        --domain vm1 sn1 \
        --diskspec vda,file=/export/images/sn1.qcow2 \
        --disk-only --atomic 

- Create an external live disk *and* memory live snapshot:

    $ virsh snapshot-create-as \
        --domain ostack-controller snap1 \
        --diskspec vda,file=/export/vmimages/disk-snap.qcow2,snapshot=external \
        --memspec file=/export/vmimages/mem-snap.qcow2,snapshot=external \
        --atomic


Merging external snapshots
~~~~~~~~~~~~~~~~~~~~~~~~~~

- Merge an entire chain (including current active image) into its base
  image 

    http://wiki.libvirt.org/page/Live-merge-an-entire-disk-image-chain-including-current-active-disk

- Efficient live disk backup with active blockcommit

    http://wiki.libvirt.org/page/Live-disk-backup-with-active-blockcommit 


Networks
--------

- To create a new libvirt network

    https://kashyapc.fedorapeople.org/virt/create-a-new-libvirt-bridge.txt

- To hot add a new NIC

    https://kashyapc.fedorapeople.org/virt/add-network-card-in-guest.txt


Monitoring Block layer QEMU events from libvirt
-----------------------------------------------

On shell 1, monitor the QEMU events from `virsh`:

    $ virsh qemu-monitor-event --pretty --loop cirrvm 
    event BLOCK_JOB_READY at 1430299466.819642 for domain cirrvm: {
        "device": "drive-ide0-0-0",
        "len": 41126400,
        "offset": 41126400,
        "speed": 0,
        "type": "mirror"
    }
    
    event BLOCK_JOB_COMPLETED at 1430299467.206985 for domain cirrvm: {
        "device": "drive-ide0-0-0",
        "len": 41126400,
        "offset": 41126400,
        "speed": 0,
        "type": "mirror"
    }


On shell 2, run a live `blockcopy` test:

    $ virsh dumpxml --inactive cirrvm > /var/tmp/cirrvm.xml

    $ virsh undefine cirrvm

    $ virsh blockcopy cirrvm hda /export/copy-cirrvm-0.3.3.qcow2 \
        --wait --verbose --shallow --finish
    Block Copy: [100 %]
    Successfully copied

    $ virsh define /var/tmp/cirrvm.xml