Detailed Instructions on Copying VMs using blocksync.py
These instructions apply to a VM using a LVM provided disk and assumes that Python is on each of the hosts
Download the blocksync.py script from https://gist.github.com/rcoup/1338263 and put on both source and destination host in your /home/user folder.
- You will need to have 'ssh' access to both machines (source and target) for your user.
You will also need to have 'sudo' access to 'root' on both machines.
Alternatively, you could do everything as root, but only if your ssh key gives you root access to at least the target machine.
** In this case, remove the user name from the command lines.
- The virtual machine is on the dom0 host known as chewie
- The destination desired in on the dom0 host known as darth and had an internal IP here 10.10.10.38 (for our example)
- In our actual case we use centos 7 as the dom0 operating system on both machines
- The VIRTUAL Machine in this instance we are moving is called LARRY
- The user doing the action is USER (which will be your name)
- DOM0 means the actual physical server
Initial steps on the source host
- Login to the dom0 host which currently has the machine (the "source" host), eg:
- Stay as your user, so don't become sudo user
*List machines with
sudo virsh --all
- Dump the machine definition using, eg:
sudo virsh dumpxml larry > larry.xml
Copy the dumped definition to the new machine (the "target" host), eg:
scp -p larry.xml 10.10.10.38:larry.xml you can change the internal ip to your destination dom0 server name
** Note: it is best to use the ip address for the target, eg:
scp -p larry.xml firstname.lastname@example.org:larry.xml
If you cannot copy due to keys the cat larry.xml and copy it
Then you can ssh into other machine and create file and paste it.
Find the size and name of the VM's disk using
sudo lvs --units B.
** The command above should show size exactly in bytes.
** The machine's disk name is in the first column of the listing, its volume group in the second, and size in the last.
** Determine the device name as /dev//
** Check it with a 'll' command
For example, in this output:
vm_larry vg1 -wi-ao---- 69793218560B
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
lv_root vg1 -wi-ao---- 53687091200B
lv_swap vg1 -wi-ao---- 17179869184B
vm_vsrv1 vg1 -wi-ao---- 193273528320B
vm_vsrv10 vg1 -wi-ao---- 64424509440B
vm_vsrv11 vg1 -wi-ao---- 161061273600B
vm_vsrv12 vg1 -wi-ao---- 204010946560B
vm_vsrv2 vg1 -wi-ao---- 140110725120B
vm_vsrv3 vg1 -wi-ao---- 128849018880B
vm_larry vg1 -wi-ao---- 69793218560B
vm_vsrv5 vg1 -wi-ao---- 257698037760B
vm_vsrv6 vg1 -wi-ao---- 64424509440B
vm_vsrv7 vg1 -wi-ao---- 161061273600B
vm_vsrv8 vg1 -wi-ao---- 64424509440B
vm_vsrv9 vg1 -wi-ao---- 214748364800B
- Disk name is 'vm_larry', volume group is 'vg1'.
- The device name is /dev/vg1/vm_larry
- Output for eg:
ls -l /dev/vg1/vm_larry is:
lrwxrwxrwx. 1 root root 8 Jan 31 13:57 /dev/vg1/vm_larry -> ../dm-11
Initial steps on the target host
- Login to the target host, eg
- Stay as your own user. i.e. don't become root.
Create a volume definition file, eg:
vi larry.domainname.com.au-vol.xml or
nano larry.domainname.com.au-vol.xmlwith the following lines:
NOTE - You will need to take the size in bytes from the original VM and put into below script. The command on the source machine for size was sudo lvs --units B
Note: this definition is for a 69793218560 Bytes disk for VM larry, change as necessary for the actual VM.
Note: the name and last part of the path should match and will be used as the new disk name.
Create the new disk from the definition, using
sudo virsh vol-create --pool centos larry.domainname.com.au-vol.xml
it will say Vol larry.domainname.com.au created from larry.domainname.com.au-vol.xml
Make the disk device file accessible:
sudo chgrp wheel /dev/mapper/centos-larry.domainname.com.au
sudo chmod g+rw /dev/mapper/centos-larry.domainname.com.au
Edit the xml definition copied over, eg:
Find the disk definition in the file (search for "source dev =") and replace the device with the one just created (you can ls /dev/centos/ to see vm), eg: /dev/drbd4 -> /dev/centos/larry.domainname.com.au
This bridge change was unique to our situation.
** Find any references to "br1" in the interface stanzas and change it to "br0" e.g. you are changing source bridge so line is like this
Final steps on the source host
Login to the source host, eg
The best practice would be to shutdown the VM on the source host before doing the final sync but doesn't need to be done. (virsh shutdown NameOfMachine)
If not already on the source host, download the blocksync.py script from https://gist.github.com/rcoup/1338263
If your username is user (for example) then copy the blocksync.py script into both machines into /home/user and chown user:user and chmod 755 the script.
- If not already on the target host, copy it there, eg:
scp -p blocksync.py email@example.com:blocksync.py
- Use it to copy the source disk to the target disk, eg
Command that does the copying
sudo -E python blocksync.py /dev/vg1/vm_larry firstname.lastname@example.org /dev/mapper/centos-larry.domainname.com.au -b 4194304
Note: the first device name is for the source host, as determined from the 'lvs' command; this one is from a [[chewie]] source host.
Note: this will destroy the contents of the target disk, make sure that /dev/mapper/centos-larry.domainname.com.au is correct!
Note: the sync will take a long time - about 100 seconds per gigabyte, ie: 90 minutes for a 60 gigabyte disk.
However, you can do a sync while the VM is in use; subsequent syncs can be up to 25 percent faster
The script will print out the parameters that it is using (there may be a message about a deprecated module, this is okay).
Next, it displays the ssh command that it is using and runs it (you will see the authorised staff only message when it does this).
During its sync, it will display a running total of blocks copied and its average speed.
Finally, it prints out a completion message with the number of seconds it took.
Things to Know
You can cancel the sync with CTRL C and restart it later by running the command again
Final steps on the target host
Note: it may be necessary to alter the details of the VM to suit the new environment.