How to Migrate the Root Filesystem to a New Disk

SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Server 12
SUSE Linux Enterprise Server 11

The root filesystem needs to be moved to a new disk or partition.

Boot the Rescue System

Use the installation media to enter rescue mode on the system. This is the safest way to copy data from the root disk as it prevents a situation where data is changing while we are copying from it. Make sure the new disk is available.
 

Copy the Data to the New Device

Copy data at the block(a) or filesystem(b) level depending on preference from the old disk to the new disk.

a. Here is an example dd command for copying at the block level:

# dd if=/dev/<old root disk> of=/dev/<new root disk> bs=64k conv=noerror,sync

NOTE: If the dd command is not being used to copy data from an entire disk to an entire disk, the partition(s) will need to be created prior to this step.

Important: The disks being copied do not need to be mounted. However, if you do mount any filesystem from the disks to be copied, please ensure that you mount these filesystems as read-only, or remount them as read-only before starting any copy using dd. This will ensure that any filesystem is copied in a consistent manner (using dd on a read/write mounted filesystem carries a major risk of introducing corruption on the target device should anything change on the source during the copy process).

b. To copy at the filesystem level, use an rsync command after mounting both the old and new root partitions. Make sure that the new root partition has a filesystem on it.

# mount /dev/<old root disk> /mnt
# mkdir /mnt2
# mount /dev/<new root disk> /mnt2
# rsync -zahP /mnt/ /mnt2/

Set the Boot Label

The boot flag needs to be set to the correct partition using either fdisk(a) or parted(b).

NOTE: This step is not always necessary. For example, this step can be skipped if the boot partition is separate from the root partition and has not changed. As another example, if dd was used on an entire disk to an entire disk in step 2, you can skip this step since the partition table will have been copied to the new disk. Finally, this step can be skipped on systems that do not use a boot label.

a. Using fdisk to label the new root partition (which contains /boot) as bootable.

# fdisk /dev/<new root disk>

From the fdisk prompt, type 'p' to list and verify the root partition is there.

Command (m for help): p

If the "Boot" column of the root partition does not have an "*" symbol then it needs to be activated. Type 'a' to toggle the bootable partition flag:

Command (m for help): a
Partition number (1-4): <root partition number>

After that use the 'p' command to verify the bootable flag is now enabled. Finally, save changes:

Command (m for help): w

(parted) quit

 

Update Bootloader Configuration

The config for GRUB(a) on SLE 11 or GRUB2(b) on SLE 12 and SLE 15 needs to be updated to boot from the new root.

NOTE: This and the remaining steps in this document will need to be done in a chroot environment on the new root disk. Knowledge Base article 7018126 covers how to use chroot in rescue mode.

Differing Environments

Environments vary and different environments can impact the necessary steps to migrate a root filesystem. Be sure to consider your own unique environment before performing the above steps. As always in administration, have backups ready and proceed with caution.
 

The dd Command

The dd command is not verbose and could take some time to complete. While it is running the command will look like it is just hanging. If needed, to verify it is still running, use the ps command on another terminal window to find the dd command's PID and use strace to follow that PID and make sure there is activity.

# ps aux | grep dd
# strace -p<process id>

After confirming activity, hit CTRL + c to end the strace command. Once the dd command is complete, the terminal prompt will return allowing for new commands to be run.