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My first try using RAID1 ended with CentOS not starting anymore - throwing me into Recovery mode. Luckily a test system

At first i set-up the raid1 which worked rather good. Later i noticed that my partitions are only 2.2TB of the available 3TB (yet using fdisk's default start/end sector - it didn't use the full HDD is this normal? edit: yes it is / using parted now)

After I noticed my thoughts were 'Yup just remove the RAID and start over again', but it seems like removing a raid is much heavier than creating one. This are just about the commands i used to delete it:

mdadm --stop /dev/md0
mdadm --zero-superblock /dev/sdb (which didn't work)
mdadm --zero-superblock /dev/sdc (also wasn't working)
mdadm --remove /dev/md0
umount /dev/md0

Then removed my entry in /etc/fstab. That was the moment i was thrown into Rescue (after reboot certainly) - so I deleted the partitions of the sdb and sdc too but it didn't change.

The errors from 'journalctl -xb' are saying:

Received SIGRTMIN+20 from PID 1694 (plymouthd)
Timed out waiting for device dev-md0.device.

Dependency failed for /data
Dependency failed for Local File Systems
Dependency failed for Mark the need to relabel after reboot.

Job rhel-autorelabel-mark.services/start failed with result 'dependency'.
Dependency failed for Migrate local SELinux policy changes from the old store structure to the new structure.

Job selinux-policy-migrate-local-changes@targeted.services/start failed with result 'dependency'.
Dependency failed for Relabel all filesystems, if necessary.

Can't understand why it's still trying to mount /dev/md0 to /data as i removed the fstab entry and the /dev/md0 device isn't available anymore.

Thanks!

  • Fixed: created partitions again with parted and recreated the RAID array. Still wouldn't know how to delete a raid, I think the main problem was that I'm missing the mdadm.conf file.. – dahe Apr 19 '18 at 17:34
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Actually I forgot to make the new filesystems with mkfs.extX /dev/sdcX, after using parted.. That's it.

Other Steps with mdadm and parted (if i need it again):
List your Block devices
lsblk

Start parted (instead of fdisk as its only capable of 2TB) in optimal mode for checking alignment errors parted -a optimal /dev/sdX

Create GPT partition (for more than 2tb again) mklabel gpt

Partition mkpart
1
ext2
2048s
-1 // don't use full space..
set 1 raid on

Create Array:
mdadm --create /dev/md/0 --level=mirror --raid-devices=2 /dev/sdb1 /dev/sdc1
yes

Un/Mounting RAID:
mount /dev/md0 /data/
umount /data/

OR add this to /etc/fstab
/dev/md0 /data ext4 defaults 0 0
and then:
mount -a

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