25 Oct 09 Move Xen Guest from loopback filesystem to LVM

Moving a Xen Guest into an LVM container from a loopback sparse image is easy enough.

You’ll need to power down the VM using xm shutdown mymachine

Once done, create the logical volume with: lvcreate –name mymachine-disk –size 10G myvg 10G should match the exact size (if not more) of your current VM. Now create the same for the swap file: lvcreate -name mymachine-swap -size 128M myvg. Now edit your machine’s config (/etc/xen/mymachine.cfg), replacing the disk part from:

disk        = [
'file:/xen/mymachine/mymachine-swap,sda1,w',
'file:/xen/mymachine/mymachine-disk,sda2,w',
]

to

disk        = [
'phy:/dev/myvg/mymachine-swap,sda1,w',
'phy:/dev/myvg/mymachine-disk,sda2,w',
]

And use dd to write the disk to your new LVM filesystem:

dd if=/xen/mymachine/mymachine-disk of=/dev/myvg/mymachine-disk
dd if=/xen/mymachine/mymachine-swap of=/dev/myvg/mymachine-swap

Remembering that you can use killall -SIGUSR1 dd at any time to gain a status update on dd’s IO.

Once done, power up your VM again with xm create mymachine.cfg

Tags: dd, disk, dom0, domu, killall, lvm, xen, xm

09 Mar 09 umount: device is busy

umount: /tmp/disk: device is busy

This is a common problem when trying to unmount a filesystem that is currently in use, especially when you have no idea what is using it!

Here’s a test..

ns3:~# cd /tmp/disk

Now we’ll create a test.sh script that will simply loop indefinitely, pausing every second as it goes.

ns3:/tmp/disk# cat test.sh
#!/bin/bash

while(true); do
sleep 1;
done

ns3:/tmp/disk# chmod +x test.sh

ns3:/tmp/disk# ./test.sh &
[1] 31460

Now test.sh is running, I’ll return to my home directory

ns3:/tmp/disk# cd ~/

Attempting to unmount /tmp/disk returns:

ns3:~# umount /tmp/disk
umount: /tmp/disk: device is busy
umount: /tmp/disk: device is busy

Assuming I don’t know that test.sh is currently running:

ns3:~# lsof +D /tmp/disk
COMMAND   PID USER   FD   TYPE DEVICE SIZE NODE NAME
test.sh 31460 root  cwd    DIR    7,0 1024    2 /tmp/disk
test.sh 31460 root  255r   REG    7,0   44   12 /tmp/disk/test.sh
sleep   31666 root  cwd    DIR    7,0 1024    2 /tmp/disk

Now I know that test.sh is running, I can issue:

ns3:~# killall test.sh
[1]+  Terminated              ./test.sh  (wd: /tmp/disk)
(wd now: ~)

Followed by:

ns3:~# umount /tmp/disk

Tags: cd, chmod, device is busy, filesystem, killall, lsof, umount, unmount