Re: [Qemu-devel] Question regarding Snapshots

[Stefan Hajnoczi]

On Wed, Feb 22, 2017 at 03:06:41PM -0600, Tim Cusack wrote:
> I have a scenario that perhaps not many have attempted, but I still hope
> that it is possible.
> 
> Scenario:
> 
> I would like to have a Base Windows 7 VM in KVM/QEMU.
> 
> I would follow the following process (confirmed it works)
> 
> 1. Shutdown running domain
> - virsh shutdown <Domain>
> 2. Remove existing disk from Domain XML:
> - virt-xml BASE --remove-device --disk target=hda
> 3. Add Correct Disk image for Snapshot to Domain XML:
> - virt-xml BASE --add-device --disk
> /var/lib/libvirt/images/BASE.qcow2,format=qcow2,target=hda,bus=ide
> 4. Create the snapshot with description
> - virsh snapshot-create-as BASE <Model>.qcow2 "OEM, Model" --disk-only
> --atomic
> 5. Start Snapshot
> - virsh start FA2BASE

This process uses libvirt instead of QEMU commands.  Adding libvirt
mailing list.

> 
> All that works, but my question and issue is this:
> 
> Can you make a snapshot, then go back to the base and ignore that snapshot
> like a closed branch, make another snapshot, and then go back and forth
> from each to each?
> 
> My reasons for needing this are that I have tools and software that doesnt
> play nice together, and would like to keep them separated on different
> snapshots, but never really need to have more than one up at a time.
> 
> This would allow me to have only 1 windows license per computer, and the
> ability to just change from tool to tool with simple front end to virsh to
> remove the disk from the .xml and add the other one.
> 
> So like this:
> Tool A is on snapshot A
> Tool B is on snapshot B
> go through steps 1-5 above to go back and forth.
> 
> I know that I can not merge things back into the base, but I really don't
> need to do that, in fact, I can throw away the tool snapshots when new
> tools come out, by making new snapshots from the base when new tools come
> out.
> 
> We have done this already, but we had an issue where the ability to write
> to the snapshots seemed to stop.
> 
> Reason unknown, everything worked one day and next could not write to any
> snapshot, but could still load the base and work on it fine.
> 
> This might be the wrong mailing list to post to, if so, could anyone point
> out a more appropriate one?
> 
> Tim

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