LVM hackery

Problem. Need to resize a LVM partition inside a Linux RHEL5 VM ware image.

Constraints. A environment where lvresize does not support online resizing. No access to a rescue disk.

First. Add the disk image to another VM image in VM player. Now startup. We can see both volumes.

vgscan
  Reading all physical volumes.  This may take a while...
  Found volume group "VolGroup00" using metadata type lvm2
  Found volume group "VolGroup00" using metadata type lvm2

Problem. We cannot address the volumes separately because they have the same name…

# Fix naming conflict, find UUIDs with vgdisplay
vgdisplay

# rename non-mounted one
vgrename abcdef-abcd-abcd-abcd-abcd-abcd-abcdef VolGroupXX

# check 
vgscan
  Reading all physical volumes.  This may take a while...
  Found volume group "VolGroupXX" using metadata type lvm2
  Found volume group "VolGroup00" using metadata type lvm2

# activate
vgchange -a y
  2 logical volume(s) in volume group "VolGroupXX" now active
  2 logical volume(s) in volume group "VolGroup00" now active

Now we can resize the “guest” disk.

# resize, check first
e2fsck -f /dev/mapper/VolGroupXX-LogVol00
                      
# resize
resize2fs /dev/mapper/VolGroupXX-LogVol00 20G

# check
mkdir m
mount /dev/mapper/VolGroupXX-LogVol00 m
df -h m

Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/VolGroupXX-LogVol00
                       20G   14G  4.8G  75% /root/m

# deactivate
umount m
vgchange -a n

Now it gets interesting… We cannot boot the VM image, this is because the boot disk has references to VolGroup00 and we renamed it to VolGroupXX. Unfortunately vgrename prevents renaming to conflicting names.

A solution: Mount the /boot partition. Extract the root disk image, edit, and repack.

sudo su

# access guest boot
mkdir boot
mount /dev/sdb1 boot

# extract
mkdir tmp
cd tmp
gzip -dc ../boot/initrd-2.6.18-53.el5.img | cpio -id

# edit - with your favourite UNIX text editor, replace VolGroup00 with VolGroupXX
emacs -nw init

# repack and replace
find ./ | cpio -H newc -o > ../boot/initrd-2.6.18-53.el5.img.cpio
gzip -c ../boot/initrd-2.6.18-53.el5.img.cpio > ../boot/initrd-2.6.18-53.el5.img

# unmount
umount ../boot