RHEL7: Booting fails for cloned SAN root disk on multipath systems

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux >= 7.2
    • dracut-033-359.el7.x86_64 and below

Issue

  • System on SAN disks boots to dracut rescue shell from cloned LUNs
  • root partition could not be found when booting from cloned SAN disks
  • dracut command doesn't update /etc/multipath.conf in initramfs
  • server doesn't boot during disaster recovery from cloned SAN disks

Resolution

  • This behavior was addressed in errata RHBA-2018:0964.

  • Workaround:

    • Systems, which shall be hardware agnostic, should have dracut-config-generic installed before they are cloned to have a more generic multipath.conf in initramfs image
    • Install dracut-config-generic and regenerate the initramfs with:
    # yum install dracut-config-generic
# dracut --regenerate-all --force

Root Cause

  • /etc/multipath.conf for the initramfs is a special version, with the current boot disk WWIDs of the system.

  • This was needed to reduce memory consumption in the kdump low memory environment, RHBZ#994702, and speeds up booting in the general case.

# lsinitrd -f etc/multipath.conf
  • ends with:
[...]

blacklist {
        wwid ".*"             
}
blacklist_exceptions {
        wwid […]
        wwid […]
}
  • These WWIDs are from the local system.

Diagnostic Steps

  • On affected systems:
# lsinitrd -f etc/multipath.conf
  • Ends with:
[...]

blacklist {
        wwid ".*"             
}
blacklist_exceptions {
        wwid […]
        wwid […]
}

  • These WWIDs are from the local system.

  • With the dracut-config-generic rpm installed and regenerated initramfs:

# lsinitrd -f etc/multipath.conf
  • Is the same output as:
# cat /etc/multipath.conf

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