If one day you decide to convert your physical server to a VM, which could be easily achieved if all its disks are presented from SAN, then don’t forget to rebuild initrd beforehand. Otherwise you would see something similar to this:
No device found Scanning and configuring dmraid supported devices Scanning logical volumes Reading all physical volumes. This may take a while... No volume groups found Activating logical volumes Volume group "VolGroup00" not found Trying to resume from /dev/VolGroup00/LogVol01 Unable to access resume device (/dev/VolGroup00/LogVol01) Creating root device. Mounting root filesystem. mount: could not find filesystem '/dev/root' Setting up other filesystems. Setting up new root fs setuproot: moving /dev failed: No such file or directory no fstab.sys, mounting internal defaults setuproot: error mounting /proc: No such file or directory setuproot: error mounting /sys: No such file or directory Switching to new root and running init unmount old /dev unmount old /proc unmount old /sys switchroot: mount failed: No such file or directory Kernel panic - not syncing: Attempted to kill init!
Also, if your SAN disks are multipathed, which is an obvious and the only correct choice, then you must (according to RedHat note) to disable multipath by editing /etc/sysconfig/mkinitrd/multipath, otherwise the system won’t boot:
# vi /etc/sysconfig/mkinitrd/multipath MULTIPATH=no
The multipath option should only be set to YES if you your root volume (/) is on a multipathed device
If multipath is enabled with root (/) on a local device, multipathing will enable at boot time and lock down the device
If the device is locked down, fsck will be unable to open it for checking
There are two options to rebuild initrd:
- Use mkinitrd or dracut, depending on the OS version you’re currently on, and pre-build a new initrd before detaching the disks from the old system.
- If the system has been already converted to a VM, .i.e. all disks from the old system have been detached and presented as RDMs to a new VM, then boot from a rescue disk, and chroot to /mnt/sysimage (if you are running RedHat or CentOS) and run mkinitrd or dracut from their. Keep in mind that /boot partition as well as /sys must be mounted in the chrooted environment or, again, your system will not fly.
mount --bind /proc /mnt/sysimage/proc mount --bind /dev /mnt/sysimage/dev mount --bind /sys /mnt/sysimage/sys