[virt-tools-list] issues with graphics driver and qcow2

[Eric Blake]

On 08/19/2017 08:32 AM, Nick Gilmour wrote:
> Hi all,
> 
> I have just installed KVM, QEMU and Virtual Machine Manager and created a
> VM with Linux Mint 18.2 on it. Everything looks good except 2 things:
> 
> 1. The graphics driver is apparently not working properly. I have tried all
> of them incl. QXL, VMVGA ( with Virtio I get error: virtio-gpu 3d
> accelaration is not supported) but I always get this popup message "running
> in software rendering mode". Besides that, I there is no option to rotate
> the display. How can I fix this?
> 
> 2. As far as I have read the difference between qcow2 and qcow storage
> format is that qcow2 is a successor of qcow. When I choose qcow2 there is
> no option for max size i.e. it has a fixed size. Is this correct? Is qcow2
> for fixed size and qcow for dynamic size?

Never choose plain 'qcow'.  It is no longer maintained, and PAINFULLY slow.

qcow2 is actively maintained, and often has performance close to
bare-metal; there are further optimizations coming down the pipeline.

qcow2 images CAN be resized; in fact, it is one of the few formats that
can actually be resized while qemu is running a guest image (the old
qcow image format can only be resized offline, not while qemu is
running).  You get different behaviors depending on whether you choose
to pre-allocate your qcow2 file (occupies more storage up front, but
guest accesses don't have to allocate more) or not (smaller file up
front, but allocations are a bit more expensive, but a LOT faster than
qcow ever was).  Part of the optimizations being proposed in upstream
qemu development is making qcow2 less prone to fragmentation issues that
might degrade performance over time.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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