13.8. Converting a root filesystem to
LVM 1
 | Backup Your System |
|---|
| |
It is strongly recommended that you take a full backup of your
system before attempting to convert to root on LVM 1.
|
 | Upgrade Complications |
|---|
| |
Having your root filesystem on LVM 1 can significantly complicate
upgrade procedures (depending on your distribution) so it should
not be attempted lightly. Particularly, you must consider how
you will insure that the LVM 1 kernel module (if you do not have
LVM 1 compiled into the kernel) as well as the vgscan/vgchange
tools are available before, during, and after the upgrade.
|
| Recovery Complications |
|---|
| |
Having your root filesystem on LVM 1 can significantly complicate
recovery of damaged filesystems. If you lose your initrd, it
will be very difficult to boot your system. You will need to
have a recover disk that contains the kernel, LVM 1 module, and
LVM 1 tools, as well as any tools necessary to recover a
damaged filesystem.
Be sure to make regular backups and have an up-to-date
alternative boot method that allows for recovery of LVM 1.
|
In this example the whole system was installed in a single root
partition with the exception of /boot. The system had a 2 gig disk
partitioned as:
/dev/hda1 /boot
/dev/hda2 swap
/dev/hda3 /
|
The / partition covered all of the disk not used by /boot and swap.
An important prerequisite of this procedure is that the root
partition is less that half full (so that a copy of it can be
created in a logical volume). If this is not the case then a
second disk drive should be used. The procedure in that case is
similar but there is no need to shrink the existing root partition
and /dev/hda4 should be replaced with (eg) /dev/hdb1 in the
examples.
To do this it is easiest to use GNU parted. This software allows
you to grow and shrink partitions that contain filesystems. It is
possible to use resize2fs and fdisk to do this but GNU parted makes
it much less prone to error. It may be included in your
distribution, if not you can download it from
ftp://ftp.gnu.org/pub/gnu/parted.
Once you have parted on your system AND YOU HAVE BACKED THE SYSTEM
UP:
13.8.1. Boot single user
Boot into single user mode (type linux S at
the LILO prompt) This is important. Booting single-user ensures
that the root filesystem is mounted read-only and no programs
are accessing the disk.
13.8.2. Run Parted
Run parted to shrink the root partition Do this so there is room
on the disk for a complete copy of it in a logical volume. In
this example a 1.8 gig partition is shrunk to 1 gigabyte
This displays the sizes and names of the partitions on the disk
# parted /dev/hda
(parted) p
.
.
.
|
Now resize the partition:
(parted) resize 3 145 999
|
The first number here the partition number (hda3), the second is
the same starting position that hda3 currently has. Do not
change this. The last number should make the partition around
half the size it currently is.
Create a new partition
(parted) mkpart primary ext2 1000 1999
|
This makes a new partition to hold the initial LVM 1 data. It
should start just beyond the newly shrunk hda3 and finish at the
end of the disk.
Quit parted
13.8.3. Reboot
Reboot the system
13.8.4. Verify kernel config options
Make sure that the kernel you are currently running works with
LVM 1 and has CONFIG_BLK_DEV_RAM and CONFIG_BLK_DEV_INITRD set in
the config file.
13.8.5. Adjust partition type
Change the partition type on the newly created partition from
Linux to LVM (8e). Parted doesn't understand LVM 1 partitions so
this has to be done using fdisk.
# fdisk /dev/hda
Command (m for help): t
Partition number (1-4): 4
Hex code (type L to list codes): 8e
Changed system type of partition 4 to 8e (Unknown)
Command (m for help): w
|
13.8.6. Set up LVM 1 for the new scheme
Initialize LVM 1 (vgscan)
Make the new partition into a PV
create a new volume group
Create a logical volume to hold the new root.
# lvcreate -L250M -n root vg
|
13.8.7. Create the Filesystem
Make a filesystem in the logical volume and copy the root files
onto it.
# mke2fs /dev/vg/root
# mount /dev/vg/root /mnt/
# find / -xdev | cpio -pvmd /mnt
|
13.8.8. Update /etc/fstab
Edit /mnt/etc/fstab on the new root so that / is mounted on
/dev/vg/root. For example:
/dev/hda3 / ext2 defaults 1 1
|
becomes:
/dev/vg/root / ext2 defaults 1 1
|
13.8.9. Create an LVM 1 initial RAM disk
Make sure you note the name that lvmcreate_initrd calls the
initrd image. It should be in /boot.
13.8.10. Update /etc/lilo.conf
Add an entry in /etc/lilo.conf for LVM 1.
This should look similar to the following:
image = /boot/KERNEL_IMAGE_NAME
label = lvm
root = /dev/vg/root
initrd = /boot/INITRD_IMAGE_NAME
ramdisk = 8192
|
Where KERNEL_IMAGE_NAME is the name of your LVM 1 enabled kernel,
and INITRD_IMAGE_NAME is the name of the initrd image created by
lvmcreate_initrd. The ramdisk line may need to be increased if
you have a large LVM 1 configuration, but 8192 should suffice for
most users. The default ramdisk size is 4096. If in doubt check
the output from the lvmcreate_initrd command, the line that
says:
lvmcreate_initrd -- making loopback file (6189 kB)
|
and make the ramdisk the size given in brackets.
You should copy this new lilo.conf onto /etc in the new root fs
as well.
# cp /etc/lilo.conf /mnt/etc/
|
13.8.11. Run LILO to write the new boot sector
13.8.12. Reboot to lvm
Reboot - at the LILO prompt type "lvm"
The system should reboot into Linux using the newly created
Logical Volume.
If that worked then you should make lvm the default LILO boot
destination by adding the line
in the first section of /etc/lilo.conf
If it did not work then reboot normally and try to diagnose the
problem. It could be a typing error in lilo.conf or LVM 1 not
being available in the initial RAM disk or its kernel. Examine
the message produced at boot time carefully.
13.8.13. Add remainder of disk
Add the rest of the disk into LVM 1. When you are happy with this
setup you can then add the old root partition to LVM 1 and spread
out over the disk.
First set the partition type to 8e(LVM)
# fdisk /dev/hda
Command (m for help): t
Partition number (1-4): 3
Hex code (type L to list codes): 8e
Changed system type of partition 3 to 8e (Unknown)
Command (m for help): w
|
Convert it into a PV and add it to the volume group:
# pvcreate /dev/hda3
# vgextend vg /dev/hda3
|
