Re: [Xen-users] Questions on qcow, qcow2 versus LVM

["Matthew Law" <matt@xxxxxxxxxxxxxxxxxx>]

Thanks for the reply - interesting that you don't have the same problem as
I do.  Maybe it is an error or ommission in my scripts?  Here are the
commands that are run to provision a domU called 'myvm' with 10GB and
512MB of swap (dom0 is CentOS 5.4 with xen 3.4.1 from the Gitco
repositories):

# domU backing store
lvcreate -C y -L 10G -n myvm VolGroupVM
parted /dev/VolGroupVM/myvm mklabel msdos
parted /dev/VolGroupVM/myvm mkpartfs primary ext2 0 1024000
kpartx -p "" -av /dev/VolGroupVM/myvm
tune2fs -j /dev/mapper/myvm1
kpartx -d /dev/VolGroupVM/myvm

# domU swap
lvcreate -C y -L 512 -n myvm-swap VolGroupVM
parted /dev/VolGroupVM/myvm-swap mklabel msdos
parted /dev/VolGroupVM/myvm-swap mkpartfs primary linux-swap 0 512
mkswap /dev/mapper/VolGroupVM-myvm--swapp1
lvscan | sort | grep ${NAME}

Then it is basically a case of (from memory):

mount -t ext3 /dev/mapper/myvm1 /mnt/vminstall
tar -xzf /home/vmimages/image.tar.gz -C /mnt/vminstall
umount /mnt/vminstall

And the domu config file looks like this:

#  -*- mode: python; -*-
name = "myvm"
maxmem = 512
memory = 512
vcpus = 1
disk = [ "phy:/dev/VolGroupVM/myvm,xvda,w",
"phy:/dev/VolGroupVM/myvm-swap,xvdb,w" ]
vif = [ "mac=ae:00:59:15:1a:0b,ip=192.168.1.11,vifname=vifmyvm0" ]
kernel = "/usr/lib/xen/boot/pv-grub-x86_32.gz"
extra = "(hd0,0)/boot/grub/menu.lst"
on_poweroff = "destroy"
on_reboot   = "restart"
on_crash    = "restart"

I have cobbled together these commands based on what I have read at
various places.  Have I screwed up somewhere?


Many thanks,

Matt.

On Thu, December 24, 2009 2:24 pm, Fajar A. Nugraha wrote:
> On Thu, Dec 24, 2009 at 9:04 PM, Matthew Law <matt@xxxxxxxxxxxxxxxxxx>
> wrote:
>> I do care about space saving but would trade a little for flexibility
>> and
>> performance.
>
> Good to hear that. So at least we can rule out LVM snapshot problems.
> At least for now.
>
>>  The dom0 in question has 8 disks on an Adaptec 5805Z
>> controller split into a 2 disk RAID1 volume for the OS and a 6 disk
>> RAID6
>> volume for domU storage and vm images.  I don't want to use individual
>> disks or create scads of partitions for each domU.
>
> I use LVM for domU disks as well. Never had the problem you mentioned.
>
>> I have a bunch of shell scripts to
>> provision domUs by creating an LV, formatting it, mounting it and
>> untarring the template image into it.
>
> That's basically what I do. I use RHEL 5.4, some with builtin Xen,
> others with Gitco's Xen rpm.
> You mentioned about disklabels and partitions. Does that mean you use
> kpartx? Did you remember to delete the mappings later using "kpartx
> -d"?
>
> I seriously suspect your problem is related to kpartx. Try changing
> your setup a little bit so that it maps LVs as partition instead of
> disks. Something like this on your domU config file:
>
> disk =        [
>       'phy:/dev/vg/rootlv,xvda1,w',
>       'phy:/dev/vg/swaplv,xvda2,w',
>       ]
>
> you could use s/hda1 instead of xvda1, if your existing domU already
> use that. There shouldn't be any change necessary to your domU tar
> image (including fstab or initramfs) if you don't use LVM on domU side
> as well.
>
> After a successful series of lvcreate - mkfs - mount - untar - unmount
> - xm create - xm destroy - lvremove, that should at least narrow down
> your problem.


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