[Discuss] Virt-Manager

[markw at mohawksoft.com (markw at mohawksoft.com)]

Let me back up.

QEMU is the actual emulation software. KVM is a management layer on top of
that. lib-virt AFAIK work on top of KVM. The virt-manager package sits on
top of that.

Couple things. "Paravirtualization" is what you really want. You want
x86[_64] code running on x86[_86] hardware. QEMU will use the
virtualization and isolation features of the kernel to run the software
"as is" and trap privileged instructions. You can get "near native" speed.

You also want to use the VirtIO drivers from within the VM

[16:08:36] dut:~ # lspci | grep -i virtio
00:03.0 Ethernet controller: Red Hat, Inc. Virtio network device
00:06.0 Communication controller: Red Hat, Inc. Virtio console
00:07.0 SCSI storage controller: Red Hat, Inc. Virtio block device
00:08.0 Unclassified device [00ff]: Red Hat, Inc. Virtio memory balloon
00:0b.0 SCSI storage controller: Red Hat, Inc. Virtio block device
00:0c.0 SCSI storage controller: Red Hat, Inc. Virtio block device
00:0d.0 SCSI storage controller: Red Hat, Inc. Virtio block device

[16:18:04] dut:~ # grep Hypervisor /var/log/dmesg
[    0.000000] Hypervisor detected: KVM

[16:20:12] dut:~ # dmidecode -s system-manufacturer
QEMU
[16:20:27] dut:~ # dmidecode -s system-product-name
Standard PC (i440FX + PIIX, 1996)

This means that I am not emulating a controller. I/O to the network or
disk directly interfaces to the hypervisor's system without emulating
something stupid like emulex, intel, or etc.

The qcow2 is a copy-on-write (cow) format. Every write to the qcow2 file
is multiplied. If you use a raw file, you lose some of the flexibility of
the qcow2 format, but speed is improved.

You can shut down the VM and use "qemu-image convert" to go from qcow2 to
raw.

You can edit the vm definition using virt-manager, edit the disk, and
click the xml tab, change "type" from "qcow2" to "raw" and update the file
name.

> Virt-manager created it as a .qcrow2 by default, did not know what that
> was. There was also an indication that 'the KVM package' was not
> installed and as a result, it would run slowly. I would have expected
> the installation of virt-manager to also pull in all required
> dependencies. Debian does not provide a package named 'kvm' and
> searching using that string under Description & Name with Synaptic,
> found no such packages that looked like it would install KVM.
>
> I believe the file system it is using, is ext4.
>
>
> On 10/20/21 3:00 PM, markw at mohawksoft.com wrote:
>> I use KVM all the time and manage it with virt-manager.
>>
>> (1) Make sure that network and disk use VirtIO para-virtual driver, do
>> not
>> emulate physical devices.
>>
>> (2) Don't use qcow2, its really slow. Pre-allocate your boot drive:
>>
>> touch myboot.raw
>> truncate -s SIZE myboot.raw
>>
>> The above will let you define a large thin-provisioned disk.
>>
>> If you have LVM or ZFS you can create a logical volume or zvol, but I
>> think the thin provisioned "sparse" file may be faster because of the
>> double caching.
>>
>>> On 10/18/21 9:20 PM, Edward wrote:
>>>> I missed a setting, found it afterwards, it defaults to Virtual
>>>> Network
>>>> (NAT) and the box to start it automatically was initially not checked.
>>>>
>>>> It's working now.
>>>>
>>> And it (take your pick):
>>>
>>>    * is slow as molasses
>>>    * runs at a snail's pace
>>>
>>>
>>> Not even worth using. Gnome Boxes on Fedora 33 ran far better and
>>> faster
>>> than Virt Manager does on Debian.
>
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