Hello, I installed a new Centos 8 distribution with 2 RAID1 mirrors. I want to be able to boot to either of the disks in case one fails. One boots, but not the other. Is there a way to enable this functionality? In previous distributions, either disk seemed to be able to boot. This is some info on my setup. Thanks.

[root@localhost ~]# cat /proc/mdstat
Personalities : [raid1]
md125 : active raid1 sdb2[1] sda3[0]
1047552 blocks super 1.2 [2/2] [UU]
bitmap: 0/1 pages [0KB], 65536KB chunk

md126 : active raid1 sdb1[1] sda2[0]
31246336 blocks super 1.2 [2/2] [UU]

md127 : active raid1 sdb3[1] sda4[0]
3874570240 blocks super 1.2 [2/2] [UU]
bitmap: 4/29 pages [16KB], 65536KB chunk

unused devices: <none>
[root@localhost ~]# cat /etc/fstab

#
# /etc/fstab
# Created by anaconda on Wed Jan 13 19:41:53 2021
#
# Accessible filesystems, by reference, are maintained under '/dev/disk/'.
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info.
#
# After editing this file, run 'systemctl daemon-reload' to update systemd
# units generated from this file.
#
UUID=ef06be6d-d895-4da5-b597-c69cace09da4 / xfs defaults 0 0
[root@localhost ~]#
0 0
UUID=a3077ef9-f8c1-4807-acf9-86b501fb9490 none swap defaults 0 0
[root@localhost ~]# df
Filesystem 1K-blocks Used Available Use% Mounted on
devtmpfs 16309916 0 16309916 0% /dev
tmpfs 16329824 0 16329824 0% /dev/shm
tmpfs 16329824 9060 16320764 1% /run
tmpfs 16329824 0 16329824 0% /sys/fs/cgroup
/dev/md127 3872678360 28960048 3843718312 1% /
/dev/md125 1041288 202008 839280 20% /boot
tmpfs 3265964 0 3265964 0% /run/user/0
[root@localhost ~]#

Should be as simple as "grub-install /dev/sdb" all things being equal. Mind you, I haven't done this on a UEFI/systemd setup; never had the need. The fact that booting with just one disk works shows the initrd is setup to handle degraded (as it should), so hopefully the above should be a simple fix.

1 members found this post helpful.

Hello, thank you. It's a little confusing to me. I tried grub2-install and got this:

[root@localhost /]# grub2-install /dev/sdb
Installing for i386-pc platform.
grub2-install: warning: ../grub-core/partmap/gpt.c:192:this GPT partition label contains no BIOS Boot Partition; embedding won't be possible.
grub2-install: error: embedding is not possible, but this is required for RAID and LVM install.

It seems like it needs a BIOS boot partition. When we set RAID up there was 1 BIOS boot partition that Centos Stream (8) demanded. It was only on 1 partition, and it wouldn't let us mirror it. I wonder if it doesn't like the UEFI setup on our somewhat old motherboard. However, it won't boot on a BIOS-only mobo. I think I'm going to try the install again with a newer motherboard, and hopefully it won't put the BIOS boot partition in.

Thanks.

for grub to install to a gpt disk a 1M partition cleared/unformatted flagged bios-boot/bios-grub is required. On a few distros, don't remember which, adding --force will force grub to install to a gpt disk without the biosgrub partition.

Thanks. I think what my main problem was is that I didn't boot the USB flash drive installer into UEFI mode. Doing that allowed me to create RAID1 partitions for /boot/efi. It booted fine with both disks, but then when I tried to run single disk experiments, it didn't boot from either disk. At least BIOS boot booted from one of the disks.

I'll look into suggestions here about trying to get BIOS boot working with RAID1. However, Censos Stream seems a bit dicey to me at this point. I may do a Centos 7 install and wait for Rocky Linux.

Thank you.