User feedback

User feedback

[rob wilco]

Hello,

I have been using KVM on debian 4.1 lenny with several virtual
machines (debian 4.0 etch, fedora 7, centos4) every day for work for
the past two weeks. The machine is a Dell Optiplex 745 with an Intel
Core Duo 2.

What I like the most is the simplicity of the set up. The wiki page on
debian is short, super clear and correct.
(kvm.qumranet.com/kvmwiki/Debian)

Compared to Xen, I like the fact that I keep my debian kernel and
drivers. It is less invasive: 'modprobe kvm-intel' is really
convenient. Also, compared to Xen it works 'out of the box'.

VM configuration with command line options also helps to get a VM
running in a few seconds. Compared to VMware, the creation of a new VM
is easier: less mandatory parameters. Except maybe for the '-net'
parameters which are not cristal clear to me.

So far, the host and VMs have never crashed which is a great confort
when you want it to 'just work' and focus on your job.

Also, there are few things that I find not easy to do :

 - I can't mount the logical volume where the VM sits, I guess it is
the qcow format not 'recognised' by mount. It is cool to be able to do
that with Xen or Vserver, you do not have to boot the machine or read
the docs on the qcow format to check out a file.

 - I can't launch kvm from a console and still see the kernel boot
message (i'll dig into the qemu options someday)

 - the VM will almost pause when you're not watching! It is quite
obvious on a VM boot:  when you're working on another virtual desktop
! Does it have something to do with the debian kernel being maybe
optimized for 'desktop usage' and the active window getting most of
the responsiveness? I tried to 'nice' kvm without much noticeable
effect.

 - I don't understand the output of ifconfig when there is a bridge
involved. The bridge is said transparent but it is the only interface
carrying with the real IP address. It is a bit confusing and does not
help network troubleshootings. I know it is standard linux bridging
but if you can put a super clear wiki page on bridging designed on use
cases that would help numerous VM users.

We work in the Telco field and see the virtualization tools mainly for
development and tests purpose. Production architecture based on
virtualization are in the roadmap though.

I guess the company will go VMWare as it has an ecosystem of third
party companies offering expertise on VMWare deployment architectures.
If the techies have a say, we will propose Xen or Vserver as these two
technologies have
several years of experience and user feedback.

Thank you for your work, have a good day,

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Re: User feedback

[Anthony Liguori]

rob wilco wrote:
> Hello,
>
> I have been using KVM on debian 4.1 lenny with several virtual
> machines (debian 4.0 etch, fedora 7, centos4) every day for work for
> the past two weeks. The machine is a Dell Optiplex 745 with an Intel
> Core Duo 2.
>
> What I like the most is the simplicity of the set up. The wiki page on
> debian is short, super clear and correct.
> (kvm.qumranet.com/kvmwiki/Debian)
>
> Compared to Xen, I like the fact that I keep my debian kernel and
> drivers. It is less invasive: 'modprobe kvm-intel' is really
> convenient. Also, compared to Xen it works 'out of the box'.
>
> VM configuration with command line options also helps to get a VM
> running in a few seconds. Compared to VMware, the creation of a new VM
> is easier: less mandatory parameters. Except maybe for the '-net'
> parameters which are not cristal clear to me.
>
> So far, the host and VMs have never crashed which is a great confort
> when you want it to 'just work' and focus on your job.
>
> Also, there are few things that I find not easy to do :
>
>  - I can't mount the logical volume where the VM sits, I guess it is
> the qcow format not 'recognised' by mount. It is cool to be able to do
> that with Xen or Vserver, you do not have to boot the machine or read
> the docs on the qcow format to check out a file.
>   

http://hg.codemonkey.ws/qemu-nbd/

This will let you expose a qcow file (or an individual partition within 
a qcow file) as an NBD server which you can then mount on your host.  A 
bit round-about but it gets the job done.

>  - I can't launch kvm from a console and still see the kernel boot
> message (i'll dig into the qemu options someday)
>   

If you configure your guest to output to the serial console (add 
console=ttyS0 to the kernel command line in menu.lst), then you only 
need to pass -serial stdio when launching the VM.

>  - the VM will almost pause when you're not watching! It is quite
> obvious on a VM boot:  when you're working on another virtual desktop
> ! Does it have something to do with the debian kernel being maybe
> optimized for 'desktop usage' and the active window getting most of
> the responsiveness? I tried to 'nice' kvm without much noticeable
> effect.
>   

Yeah, this is a weird SDL issue.  I'm not really sure why it happens.

>  - I don't understand the output of ifconfig when there is a bridge
> involved. The bridge is said transparent but it is the only interface
> carrying with the real IP address. It is a bit confusing and does not
> help network troubleshootings. I know it is standard linux bridging
> but if you can put a super clear wiki page on bridging designed on use
> cases that would help numerous VM users.
>   

http://kvm.qumranet.com/kvmwiki/AnthonyLiguori/Networking

This is for Ubuntu but it probably works in Debian too.  It uses NAT 
instead of bridging and it is what I use on my desktop.

Regards,

Anthony Liguori

> We work in the Telco field and see the virtualization tools mainly for
> development and tests purpose. Production architecture based on
> virtualization are in the roadmap though.
>
> I guess the company will go VMWare as it has an ecosystem of third
> party companies offering expertise on VMWare deployment architectures.
> If the techies have a say, we will propose Xen or Vserver as these two
> technologies have
> several years of experience and user feedback.
>
> Thank you for your work, have a good day,
>
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> _______________________________________________
> kvm-devel mailing list
> kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
> https://lists.sourceforge.net/lists/listinfo/kvm-devel
>
>   


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Re: User feedback

[Avi Kivity]

rob wilco wrote:
> Hello,
>
> I have been using KVM on debian 4.1 lenny with several virtual
> machines (debian 4.0 etch, fedora 7, centos4) every day for work for
> the past two weeks. The machine is a Dell Optiplex 745 with an Intel
> Core Duo 2.
>
> What I like the most is the simplicity of the set up. The wiki page on
> debian is short, super clear and correct.
> (kvm.qumranet.com/kvmwiki/Debian)
>
> Compared to Xen, I like the fact that I keep my debian kernel and
> drivers. It is less invasive: 'modprobe kvm-intel' is really
> convenient. Also, compared to Xen it works 'out of the box'.
>
> VM configuration with command line options also helps to get a VM
> running in a few seconds. Compared to VMware, the creation of a new VM
> is easier: less mandatory parameters. Except maybe for the '-net'
> parameters which are not cristal clear to me.
>
> So far, the host and VMs have never crashed which is a great confort
> when you want it to 'just work' and focus on your job.
>
> Also, there are few things that I find not easy to do :
>
>  - I can't mount the logical volume where the VM sits, I guess it is
> the qcow format not 'recognised' by mount. It is cool to be able to do
> that with Xen or Vserver, you do not have to boot the machine or read
> the docs on the qcow format to check out a file.
>   

qcow is just one of the formats supported by kvm.  You can easily use a 
logical volume for your disks, just as with Xen.

>  - I can't launch kvm from a console and still see the kernel boot
> message (i'll dig into the qemu options someday)
>   

You can, using the '-serial' option.

>  - the VM will almost pause when you're not watching! It is quite
> obvious on a VM boot:  when you're working on another virtual desktop
> ! Does it have something to do with the debian kernel being maybe
> optimized for 'desktop usage' and the active window getting most of
> the responsiveness? I tried to 'nice' kvm without much noticeable
> effect.
>   

This has been reported before.  I can't understand why it happens 
though.  Can you check if it happens with the -no-kvm switch?

>
> We work in the Telco field and see the virtualization tools mainly for
> development and tests purpose. Production architecture based on
> virtualization are in the roadmap though.
>
> I guess the company will go VMWare as it has an ecosystem of third
> party companies offering expertise on VMWare deployment architectures.
> If the techies have a say, we will propose Xen or Vserver as these two
> technologies have
> several years of experience and user feedback.
>
>   

One thing that kvm uniquely supports is the ability to run real-time 
applications alongside virtual machines.  I don't think any other 
solution provides that facility.


-- 
Any sufficiently difficult bug is indistinguishable from a feature.


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Re: User feedback

[John Clemens]

On Fri, 2007-10-05 at 07:52 -0500, Anthony Liguori wrote:

> http://hg.codemonkey.ws/qemu-nbd/
> 
> This will let you expose a qcow file (or an individual partition within 
> a qcow file) as an NBD server which you can then mount on your host.  A 
> bit round-about but it gets the job done.

You just made my day. I've been threatening to do the same thing for
weeks :)  A couple of questions if you don't mind:

- I was a bit confused by the statement on the nbd homepage:

"Read-write nbd with client and server on same machine has a rather
fundamental problem: when the system is short of memory, it tries to
write back dirty pages. So the nbd client asks the nbd server to write
back data, but as nbd-server is a userland process, it may require
creating dirty pages to fullfill the request."

The above makes sense, and the README in the source says this is not a
problem on SMP systems since there's more than one kblockd flush
thread... which makes less sense (why can't both kblockd's be blocked in
this way?)

Does qemu-nbd address this, perhaps by opening the qcow file with O_SYNC
or something?  or is this still a problem?

- There's no license file with the code, I'm assuming it's GPL since you
use qemu code directly?

Thanks for writing such a useful bit of software!
john.c


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Re: User feedback

[Wolfram Gloger]

Anthony Liguori writes:

>http://kvm.qumranet.com/kvmwiki/AnthonyLiguori/Networking
>
>This is for Ubuntu but it probably works in Debian too. It uses NAT
>instead of bridging and it is what I use on my desktop.

Good advice, but why use a bridge interface _at all_ in this case?
I have the following in /etc/network/interfaces:

iface tap0 inet static
        address 192.168.0.1
        netmask 255.255.255.0
	pre-up iptables-setup-for-masq

and in my qemu-ifup (or rather kvm-ifup):

#!/bin/sh
/sbin/ifconfig $1 0.0.0.0 up
/sbin/ifup $1
exit 0

and that is all..  No more need for any bridging.

BTW I think it would be an important feature to also have
a qemu-ifdown / kvm-ifdown script to remove the iptables
rules after the tap device disappears.

Regards,
Wolfram.

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Re: User feedback

[Anthony Liguori]

Wolfram Gloger wrote:
> Anthony Liguori writes:
>
>   
>> http://kvm.qumranet.com/kvmwiki/AnthonyLiguori/Networking
>>
>> This is for Ubuntu but it probably works in Debian too. It uses NAT
>> instead of bridging and it is what I use on my desktop.
>>     
>
> Good advice, but why use a bridge interface _at all_ in this case?
>   

Because sometimes I launch more than one VM and I also wanted to be able 
to use dhcp in the guest.  But yeah, you're right, you could just 
preconfigure a bunch of tapN devices and that would solve the problem too.

Regards,

Anthony Liguori

> I have the following in /etc/network/interfaces:
>
> iface tap0 inet static
>         address 192.168.0.1
>         netmask 255.255.255.0
> 	pre-up iptables-setup-for-masq
>
> and in my qemu-ifup (or rather kvm-ifup):
>
> #!/bin/sh
> /sbin/ifconfig $1 0.0.0.0 up
> /sbin/ifup $1
> exit 0
>
> and that is all..  No more need for any bridging.
>
> BTW I think it would be an important feature to also have
> a qemu-ifdown / kvm-ifdown script to remove the iptables
> rules after the tap device disappears.
>
> Regards,
> Wolfram.
>
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>   


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