[TriLUG] grub2-install fails with error: unknown filesystem

[Ron Kelley via TriLUG]

I have done this in the past when I converted from non-raid to raid.  Hope it works for you:

Grub: 
device (hd0) /dev/sda
device (hd1) /dev/sdb
root (hd0,1)
setup (hd0)
root (hd1,1)
setup (hd1)


> On Nov 9, 2017, at 2:00 PM, Lee Fickenscher via TriLUG <trilug at trilug.org> wrote:
> 
> Greetings luggers,
> 
> I've been fruitlessly googling the issue over the last couple of days and
> I'm hoping that someone has encountered and triumphed over this issue...
> 
> Issue:
> Trying to install grub to the mbr of one of a dmraid1 mirror fails
> with error: unknown filesystem.
> 
> The preamble:
> We have a CentOS7 server with OS disks in mdraid1 partitioned thusly:
> 
> --------------------------------------
> $ sudo fdisk -l /dev/sda
> 
> Disk /dev/sda: 500.1 GB, 500107862016 bytes, 976773168 sectors
> Units = sectors of 1 * 512 = 512 bytes
> Sector size (logical/physical): 512 bytes / 4096 bytes
> I/O size (minimum/optimal): 4096 bytes / 4096 bytes
> Disk label type: dos
> Disk identifier: 0x00000000
> 
>   Device Boot      Start         End      Blocks   Id  System
> /dev/sda1            2048    67110911    33554432   fd  Linux raid
> autodetect
> /dev/sda2   *    67110912    69208063     1048576   fd  Linux raid
> autodetect
> /dev/sda3        69208064   976773119   453782528   fd  Linux raid
> autodetect
> --------------------------------------
> 
> sda1 is swap
> sda2 is /boot
> sda3 is LVM root
> 
> During setup we make sure that the MBR is written on both raid members so
> we can always boot and previously haven't had a problem.
> We had a drive fail so the drive was replaced, partition table written, and
> raid arrays synced. All was good until I tried to write the MBR.
> 
> Fix attempts:
> I've gone through untold iterations of grub2-install commands, mainly
> trying different modules and what not.
> The only clue I've gotten is when running grub2-install with --debug which
> provides:
> 
> grub2-install: info: /dev/md125 is not present.
> grub2-install: error: unknown filesystem.
> 
> However, md125 is the /boot array and it's definitely there so I'm thinking
> this may be a red herring.
> 
> I'm tempted to just use --force since it seems to be checking unrelated
> filesystems but was hoping someone with more grub experience would chime in.
> 
> Thoughts?
> 
> Thanks!
> -Lee
> -- 
> This message was sent to: Ron Kelley <rkelleyrtp at gmail.com>
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