[CentOS-virt] Re: [kvm-devel] (long) kvm and virt-manager not ready for daily usage

Izik Eidus izike at qumranet.com
Sat Sep 8 01:24:50 UTC 2007

Farkas Levente wrote:
> hi,
> in the last 2 weeks we play a lot with our new server which we but to a
> our virtual server for the development and collect some very subjective
> experience. we use kvm and virt-manager, but sometimes i'm not really
> sure about the whether it's kvm or virt-manager problem so i collect
> them together. our system:
> MB: Intel S3000AHV
> CPU: Intel Core 2 Quad CPU Q6600 @ 2.40GHz
> RAM: 8GB
> CentOS 5 x86-64 host system with:
> kernel-2.6.18-8.1.8.el5
> kmod-kvm-35-
> kvm-35-1
> libvirt-0.3.2-2
> libvirt-python-0.3.2-2
> python-virtinst-0.300.0-1
> virt-manager-0.5.0-1
> virt-top-
> virt-viewer-0.0.2-1
> kvm is not ready for production use for many reason:
> it can't reboot which imho a very basic feature, what's more can't even
> shutdown/poweroff. the centos i386 guest are not able to shutdown on the
> x86_64 host (strange the x86_64 centos and the i586 mandrake-9 are able
> to shutdown) or what's seems to be more likely it's a random think.
this issue is known and will be fix soon.
> can't give 2GB ram to any guests not even 2, but 1.9999 is ok. what's
> more i've to discover this in the hard way virt-manager gives some
> strange error message (anyway none of the virt-manager's error message
> are useful, just strange stack trace without any kind of useful info).
kvm from version 36 support above 2giga of ram (it was tested with 
32giga ram guest)
> the host see as i've 4 cpu. i've got a change to gives more cpu to the
> guest, what's more they starts, but after a few minutes running the
> system crash. not just the guest os but the host os crash without any
> kind of info, log or any useful info what was the cause of it, but hard
> reset helps:-((( first of all it's serious problem, even if it's a known
> bug and documented somewhere (but there is not any kind of docs about
> neither kvm nor virt-manager/libvirt and what i can find that very
> limited), since all of the new hvm cpu (which is required for kvm) has
> more core, so the guest can't use the real power of the cpu this means
> i've to put a lots of guests with one virtual cpu to the host or
> currently can't exploit these cpus.
> libvirt not start the guest when the host started, not saved the state
> of the guests when stopped, when restarted all guest get into shutdown
> state. may be it's just libvirt but, but if kvm not able to save it's
> guest's state that it's a real pain. this behavior not acceptable in a
> real environment.
> in virt-manager can't modify virtual cpu number of the guests
> (virt-manager crash with another unusable stacks trace). it i modify the
> xml config file by hand i've to restart libvirt in order to read it.
> even if i just modify one guest's config, but as if i restart libvirtd
> the all other guest will be killed it's another nice feature.
> from vit-manager i can't assign swap partitions (and any other device
> to the guests) during guest creation. i precreate lvm partition on the
> host for root and swap to all of our guests (about 10) but it's a real
> pain to reload libvirtd (which kills all guests) to add a new disk to
> the guest which can be used as a swap or other partition. what's more
> it'd be useful to add swap partition during install. the same thing
> apply to cdrom too.
> if i made a mistake in the libvirtd xml config file, then i don't get
> any kind of error message just libvirt don't start the given guest. no
> error message service seems to start without error and don't know what
> was the reason that the guest not start (sometimes because syntactic
> error in the config file, sometimes kvm/qemu not support it eg more then
> 2gb mem). there are unwritten unix/linux tradition eg if there are error
> during a service startup report it some log file. if a service can't
> start without error then it not start at all eg. if i've apache with 5
> virtual host but one of it's config has error then the whole httpd not
> started. it'd have to be the same with libvirt too.
> libvirt config file has all the features as qemu command line (if not it
> can't be used by advanced users)? but i don't know since there is not a
> reference docs for the config file.
> there is not a detailed reference docs about libvirtd config (and at the
> same time the gui not contains all the settings). for the the xml format
> is a bit redundant eg. "source dev", "target dev" why not just source
> and target, inside interface type='bridge' 'source bridge' why not just
> source (i've to modify two place when i'd like to switch from network to
> bride. ok these are just small cosmetic thing just mention.
> when create a new guest in virt-manager and reach the last page and
> press finish then most of the time (2 times from 3) i've got an error
> something like "can't connect to qemu" after i press ok and press again
> finish then it's able to create the new host (so always have to retry it).
> in virt-manager when a guest is shutdown and double-click on the guest
> and try to start it it's not possible. you've to select the guest in the
> main windows, right-click and start it.
> the new vnc based console is very unstable or just virt-manager not able
> to connect it. many times i double click on a guest in virt-manager i
> got the window can't connect to console while the guest are running.
> that's why i like to see again the serial console.
> we've got other virtual servers with xen and openvz, with has other
> problems but works. my conclusion is that currently kvm, libvirtd,
> virt-manager (et-mgmt-tools) seems very promising. but currently just in
> a very alpha stage using even in non mission critical but production
> environment still a very 'brave' decision. xen has a few years vantage,
> but it's at least usable in real environment.
> i'm on the these list and see what kind of problem you're working which
> is great but at the same it'd be useful to fix the most basic problems
> with these tools.
> just my 2c to these community.
thanks for all this information, this exactly what we need!

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