Kernel Boot parameter length exceed limits in multipath FCP setup during RHEL installation on IBM Z

Solution Unverified - Updated

Environment

Red Hat Enterprise Linux 9.1 for IBM Z
Red Hat Enterprise Linux 9.0 for IBM Z

Issue

Using more than one LUN during the installation of Red Hat Enterprise Linux (RHEL) with a multi-path FCP (Fibre Channel Protocol) setup, causes the kernel boot parameters to exceed the maximal supported length. This issue arises due to the LUN auto-scan behavior, which results in an excessively long kernel boot parameter string.

Resolution

  1. Install your system onto a single LUN with the default LVM setup. After installation, the boot parameters will include a valid zfcp configuration, for example, rd.zfcp=0.0.a400,0x5005076810274E12,0x0000000000000000. Do not modify this configuration.

  2. The multipathd daemon detects other LUNs and creates nodes under /dev/mapper with names starting with mpath. If the LUNs are not listed, it may be due to the LUN scan being disabled. To enable it, use the following commands:

    # grubby --update-kernel ALL --remove-args "allow_lun_scan=0"
# zipl
# reboot

  3. After reboot, add the additional LUNs to the setup by including them in the volume group. Assuming there is a LUN listed as /dev/mapper/mpathb, proceed with the following steps:
    3.1. Declare the LUN as a physical volume:

    # pvcreate /dev/mapper/mpathb

    3.2. List the volume groups to identify the correct one and extend the volume group with the new LUN:

    # vgdisplay
# vgextend rhel_vg /dev/mapper/mpathb

    3.3. By default, the installation creates logical volumes for "/" (root) and "/home". Choose which one to extend and add the LUN. For example, to extend the root logical volume:

    # lvextend -r -l +100%FREE /dev/rhel_vg/root

    3.4. To verify the changes, confirm that the logical volume has been successfully extended:

    # df -h

    The output should display the following updated size of the extended volume:

    Filesystem                Size  Used Avail Use% Mounted on
/dev/mapper/rhel_vg-root  358G   12G  347G   4% /

For more information, see Content from www.ibm.com is not included.IBM Docs.

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