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Using DMS (SUSE Distribution Migration System) on a system configured to use LVM as root filesystem

This document (000021483) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 12 SP5
SUSE Linux Enterprise Server for SAP 12 SP5

Situation

A cloud instance which has its root filesystem located on LVM while having other main OS components (ie. directories) located on separate filesystems-logical volumes (see below), needs to be upgraded to higher OS major version. The Distribution Migration System (DMS) was chosen for the upgrade/migration.

The DMS-based upgrade/migration fails.

An example of an OS installation with main OS components/directories (that is, /usr, /var here) located on separate filesystems-LVs:

# lsblk -p -n -r -o NAME,MOUNTPOINT
/dev/vda
/dev/vda1
/dev/vda2 /boot/efi
/dev/vda3
/dev/mapper/systemVG-home /home
/dev/mapper/systemVG-usr /usr
/dev/mapper/systemVG-var /var
/dev/mapper/systemVG-LVRoot /

Resolution

Officially, there is no supported path via DMS for an upgrade in this situation. However, an alternative to DMS with such a non-supported disk layout might be the offline upgrade with the installation media data unpacked on a network server. You can refer to the following guides on how to setup a source server for network installations and how to make installation media kernel to use the network installation server via linuxrc boot options:
  • https://documentation.suse.com/sles/15-SP5/html/SLES-all/cha-deployment-instserver.html
  • https://documentation.suse.com/sles/15-SP5/html/SLES-all/appendix-linuxrc.html

Cause

DMS only works with servers that have their OS on a single partition, with only /boot being supported as a separate one. The default image that we provide to Public Cloud providers was not used when initially setting up the server and the customer built their own with LVM separating each part of the OS into a different LV, which DMS considers a separate partition.

 

Additional Information

One major requirement for it is for all of the main OS components to be on the same partition, as per the official guide here:

https://documentation.suse.com/suse-distribution-migration-system/15/html/distribution-migration-system/index.html

In section 2, "Upgrade Prerequisites" we read:
 
Requirement for root filesystem

For DMS working as designed, root filesystem - "/" - and all core OS functional folders such as /var, /etc, /usr must be on a single partition. Multiple partition support, such as LVM, is limited to configurations where the separated partitions do not contain OS critical data or processes. For example, DMS will function if /home is its own partition, but not if /var is on a separate partition from root.

Additionally, in section "Caveats and Unsupported Conditions" we read the following:
 
In systems that contain multiple root file systems on different mount points only the root file system mounted on / (primary system) will be migrated.

With the above in mind, the most common LVM setup (with every OS directories in a separate LV) would be unsupported for upgrade, even if it is "technically" the same real disk partition, as DMS considers them as different partitions.

Examples of supported and non-supported LVM filesystem layouts:

Supported layout: 
# lsblk -p -n -r -o NAME,MOUNTPOINT
/dev/vda
/dev/vda1
/dev/vda2 /boot/efi
/dev/vda3
/dev/mapper/systemVG-LVRoot /

Not supported layout (see that /usr, /var, is separated from /): 
# lsblk -p -n -r -o NAME,MOUNTPOINT
/dev/vda
/dev/vda1
/dev/vda2 /boot/efi
/dev/vda3
/dev/mapper/systemVG-home /home
/dev/mapper/systemVG-usr /usr
/dev/mapper/systemVG-var /var
/dev/mapper/systemVG-LVRoot /

As you can see in the above example, the difference is between whether the different OS components are kept in different LVs, or are nested under the main "/" LV. Only a separate /boot partition is supported by DMS, which should be kept in mind before launching an upgrade.

Disclaimer

This Support Knowledgebase provides a valuable tool for SUSE customers and parties interested in our products and solutions to acquire information, ideas and learn from one another. Materials are provided for informational, personal or non-commercial use within your organization and are presented "AS IS" WITHOUT WARRANTY OF ANY KIND.

  • Document ID:000021483
  • Creation Date: 03-Jul-2024
  • Modified Date:06-Aug-2024
    • SUSE Linux Enterprise Server
    • SUSE Linux Enterprise Server for SAP Applications

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