View Full Version : [all variants] VM-Builder: 'unpacking' takes a lot of time...

March 30th, 2011, 12:42 PM
(I know it's a double post [showthread.php?p=10614120],
but I don't know how to move a question accross Categories.)

Hi Hi Everybody,

after some testing with the vmbuilder AND a local mirror
with all the packages, the system still needs more than
12 minutes for a clean and minimum VM-image...

Is there a way to speed this proces up?

With the --debug option I found out that the 'unpacking'
task takes, by far, the most time of building a VM...
(some people think its the EXT4 on the host !??)


I'm testing on three Ubuntu Server (10.04) KVM/QEmu Hosts
on three new Dell PowerEdge R310 RackServers.

The 64bit host os's are installed on two 2Tb mirrored SataHDDs
with Ext4.

Thx in Advanced for any ideas..!!

March 31st, 2011, 05:21 PM
I know it for SURE..!

When I change the /tmp of the host OS from EXT4 to EXT3,
my vmbuilder builds the same VM in less than 4 minutes!!!!!
(in stad of more than 12 minutes)

Now I only have an other problem :sad:

When I build to a RAW logica volume (lvm),
the GUEST OS gives the following error:

EXT4-fs error (device sda1): ext4_mb_generate_buddy:
EXT4-fs group 2: 3431 blocks in bitmap, 3597 in gd

This looks like an conversion error from EXT3 to EXT4
on the guest OS!??

By the way...
When I build to a QCOW2 file, everything is/looks fine!!!

April 1st, 2011, 01:02 PM
Some extra info about EXT3 and EXT4 partition:
https://wiki.ubuntu.com/LucidLynx/ReleaseNotes#Performance regressions with ext4 under certain workloads

April 2nd, 2011, 06:55 PM
Sorry don't have much info to help here .. but please keep us informed of your findings :)

April 4th, 2011, 08:39 AM
Hi Kim,
I will keep this topic informed...

You could also subscribe to the bug report I made friday:

For now, I build my VM's the following way:

1.) VMBuilder (with the EXT3 /tmp partition) to a QCow2 file
2.) Convert the QCow2 file to a RAW file
3.) Create a new LVM logical volume
4.) sudo dd if=disk0.raw bs=512k of=/dev/vg-1/VM01-Disk0 (don't forget the option bs=512k !!)
5.) Minor adjustment to the xml in /etc/libvirt/qemu/

<disk type='block' device='disk'>
<driver name='qemu' type='raw' cache='none'/>
<source dev='/dev/vg-1/VM01-Disk0'/>
<target dev='vda' bus='virtio'/>

6.) :-) Done!

Today I'll try to script this...
Only #5 will be (for me) a difficult one.

By the way!
Some people have the following problem with VMBuilder:

"First everything seems to work ok, but soon after certain volume of traffic goes through the thing will freeze for a while. For example, I start copying 500 mb file. I will get 200 MB done superfast (50MB/s). Then everything will freeze for a while. After that copying resumes a bit slower for a few seconds and again, everything freezes."

This is because the QCow2 files. When you use RAW files or (just like me) a LVM logical volume. This problem is solved...