[Xen-users] live migration, loopback devices & NFS.

Miguel Gómez
Tue, 12 Jul 2005 16:42:51 -0000

Hello people,
I am trying to do is a live migration between two hosts in my subnet.
One of them (XENmaster) has NFS service with this line in
/etc/exports:

/xen    192.168.50.0/255.255.255.0(rw,sync,no_root_squash)

In the other machine (XENslave) I mount that directory with this line:

mount -t nfs XENmaster:/xen    /xen

So in both machines I see the same in /xen directory. In that
directory I have the loop back devices:

XENmaster:/xen# ls -l
total 286664
-rw-r--r--  1 root root 2139119616 2005-07-12 17:56 vmDebian2
-rw-r--r--  1 root root  268436480 2005-06-30 18:31 vmDebian2Swap


XENslave:/xen# ls -l
total 286664
-rw-r--r--  1 root root 2139119616 2005-07-12 17:56 vmDebian2
-rw-r--r--  1 root root  268436480 2005-06-30 18:31 vmDebian2Swap

If I try to create a virtual machine in XENslave (The machine that is
NOT running NFS), I get that VM starts normally but when it tries to
check the filesystem it finds a problem:

IP-Config: Complete:
      device=eth0, addr=192.168.50.213, mask=255.255.255.0, gw=255.255.255.255,
     host=192.168.50.213, domain=, nis-domain=(none),
     bootserver=1.2.3.4, rootserver=1.2.3.4, rootpathEXT3-fs warning: mounting
fs with errors, running e2fsck is recommended
kjournald starting.  Commit interval 5 seconds
EXT3 FS on hda1, internal journal
EXT3-fs: mounted filesystem with ordered data mode.
VFS: Mounted root (ext3 filesystem).
Freeing unused kernel memory: 112k freed
INIT: version 2.86 booting
Activating swap.
Checking root file system...
fsck 1.37 (21-Mar-2005)
/dev/shm/root: The filesystem size (according to the superblock) is
524288 blocks
The physical size of the device is 522246 blocks
Either the superblock or the partition table is likely to be corrupt!


/dev/shm/root: UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY.
        (i.e., without -a or -p options)

fsck failed.  Please repair manually and reboot.  Please note
that the root file system is currently mounted read-only.  To
remount it read-write:

   # mount -n -o remount,rw /

CONTROL-D will exit from this shell and REBOOT the system.

Press enter for maintenance
(or type Control-D to continue):


It seems that something is wrong with the filesystem block size:

/dev/shm/root: The filesystem size (according to the superblock) is
524288 blocks
The physical size of the device is 522246 blocks
Either the superblock or the partition table is likely to be corrupt!

But I don''t really know how to resolve this. It seems that
there''s a
problem with NFS and loopback devices, but how do I do this without
loopback devices? I can create VMs with LVM but, how do I share them?
What do you do? Has anybody there used live migration? How did you get
it?

Thank you for your  help.
 MIguel.