[et-mgmt-tools] Re: Virt-P2V problem

[Richard W.M. Jones]

On Sat, Mar 08, 2008 at 12:21:52AM -0800, Kevin Collins wrote:
> I then was able to manually mount my /root partition (before taking any
> steps in virt-p2v). So, I assumed success and went thru the steps to begin
> the migration. It again failed to mount my /root (not - it was not still
> mounted). The dmesg showed the same error again... I tried to manually mount
> another partition and saw the same error. Maybe virt-p2v is insmod'ing
> something before it tries to mount?

Yes, I know what this is.  The pertinent error is:

  EXT3-fs: blocksize 1024 too small for device blocksize 4096.

The problem is convoluted.  In order to avoid modifying the underlying
disk, we use a device mapper feature to make a writable snapshot of
the partitions that we will change (such as the root partition because
we'll change /etc/fstab).  The writable snapshot stores changes in a
ramdisk so that at next reboot all the changes magically disappear and
we haven't modified the original disk.

All well and good but the writable snapshot ends up with the same
blocksize as the ramdisk (4096 by default).  Since your filesystem is
from Fedora Core 1, it has a blocksize of 1024, and a limitation of
ext3 is that it cannot mount a filesystem with blocksize smaller than
the device blocksize.

Solution should be the following.  When the ramdisk boots, go into
grub and add:

  ramdisk_blocksize=1024

to the kernel command line.

(Doc: http://www.mjmwired.net/kernel/Documentation/ramdisk.txt)

Rich.

-- 
Richard Jones, Emerging Technologies, Red Hat  http://et.redhat.com/~rjones
virt-top is 'top' for virtual machines.  Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.
http://et.redhat.com/~rjones/virt-top