Booting into Rescue mode with USB drive on IBM Power fails

This document (000020372) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 12 SP5
SUSE Linux Enterprise Server 12 SP4

Situation

Booting into Rescue Mode using an USB drive fails.
System boots but after selecting "Rescue System" at the GRUB prompt, system fails and doesn't appear to find the installation medium, USB drive.

Linuxrc presents the following screen:

Please make sure your installation medium is available.
Choose the URL to retry.
cd:/
hd:/
Enter another URL

After using a workaround (see Additional Information), on systems with a large number of multipath devices, boot hangs at "lvm2-pvscan":

[FAILED] Failed to start LVM2 PV scan on device 65:160.
See 'systemctl status lvm2-pvscan@65:160.service' for details.
[FAILED] Failed to start LVM2 PV scan on device 69:16.
See 'systemctl status lvm2-pvscan@69:16.service' for details.

[* ] (1 of 126) A start job is running f...n device 65:160 (12s / no limit)

Resolution

A Rescue Media Update addresses both problems and the workaround in "Additional Information" won't be needed anymore.

The ISO image with the fixes to boot into Rescue Mode on POWER systems for both SLES12 SP4 and SP5 are available at the SUSE SolidDriver Program page - drivers.suse.com:

Rescue Media Update for SLE-12-SP4
and
Rescue Media Update for SLE-12-SP5

Cause

The first problem not finding the installation media is caused by:
The msdos partition entries weren't in a format/table the boot medium would recognize.
After removing some superfluous entries the msdos partition was recognized.

The second problem hanging at "lvm2-pvscan" is caused by:
The rescue environment boots with multipath disabled and LVM enabled and multipath needs to be activated before the devices are discovered and LVM is setup.
However, multipath should be enabled on systems with many multipath devices using LVM

Additional Information

To boot into the Rescue System using a USB drive, one of the following workarounds was used:
a) Specify the exact device (e.g. hd:/?device=sda)
b) Use 2 USB drives:

First USB Pendrive with (rufus) software to burn the SLES12 SP4 or SP5 installer ISO to the USB Pendrive.
Second USB Pendrive with ext4 file system and a /repo dir containing the SLES12 SP4 or SP5 installer DVD content.

Both USB Pendrive are detected in the SMS menu (System Management Services).
Select the bootable USB for boot and select "Normal Mode Boot", exit SMS, GRUB loads, select "Rescue System".
Wait for stage 2. At the linuxrc screen: select "Back", select "Start Installation", select Rescue System again and it prompts three options:

DVD / CD-ROM
Network
Hard Disk

Select Hard Disk and select the USB pendrive with the /repo on it.
On the next screen "Enter the source directory."
Provide the absolute path for repo.

Then the installer boots to the "rescue login" prompt.

Disclaimer

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