Quote Originally Posted by AAEBHolding View Post
Good, I think I could fix it after hours of desperate trying.
These 3 threads did it:
  1. https://unix.stackexchange.com/quest...left-on-device
  2. http://marc.merlins.org/perso/btrfs/...-Problems.html
  3. http://marc.merlins.org/perso/btrfs/...-Problems.html

I summarize what I did:
  1. Start the VM in the rescue mode.
  2. mount /dev/xvda2 /mnt
  3. btrfs balance start -v --full-balance /mnt

When I got Done, had to relocate 12 out of 12 chunks then it worked (1).
When I got the message
ERROR: error during balancing '/mnt' - No space left on device
There may be more info in syslog - try dmesg | tail

I had to proceed with (2).

And here, I had two different situations:
1) One VM has been completely recovered and works well even before the VM didn't start and crashed while booting - with other words the VM became void.
2) The other VM was more persistent and really tiresome. I had to find a XenServer snapshot from the VM where the VM did at least start properly even it crashed within few seconds.

Then, to check if it really works I was running some heavy disk access routines where before the VM crashed within seconds. Now, it runs without any problem.
I hope, it will remain like this.
Thanks for the feedback and good work