This tutorial explains how to convert existing single disk CentOS 7.4 system into a two disk RAID1 system without loosing data or reinstall the system. RAID 1 produces a mirrored set, which can tolerate a single disk failure. The GRUB2 bootloader is also configured in such a way that the system will still be able to boot if any of the hard drives fails.
Before starting lets familiar with our current system Configurations.
Operating System : Centos 7.4
Hard Disk partitions
2GB /boot partition as /dev/sda1 16GB / root partition as /dev/sda2 2GB swap space in /dev/sda3 Partition Type : ext4
We are adding a second identical disk /dev/sdb for raid 1 setup. The raid will be a linux software raid managed by "mdadm" . If the "mdadm" command is not available, install it using yum command. So attach the new disk in to the server mother board before proceeding with below steps.
yum install mdadm
Now lets get started. Create identical partition scheme as current disk /dev/sda
sfdisk -d /dev/sda | sfdisk /dev/sdb
Check changes or see the difference using below command.
fdisk -l
Changes partition type to Linux RAID autodetect. To do so, "fdisk" the specific hard disk.
fdisk /dev/sdb use "t" to convert all 3 partitions to "fd"
Verify the result using below command.
fdisk -l
Now we are going to create a degraded RAID1. Which means we Create RAID1 devices in degraded state because the one disk is missing, i.e. /dev/sda which is currently installed with OS and used to boot up.
In our case we have three partitions. So we are doing it for all partitions in new disk /dev/sdb
mdadm --create /dev/md0 --level=1 --raid-devices=2 missing /dev/sdb1 mdadm --create /dev/md1 --level=1 --raid-devices=2 missing /dev/sdb2 mdadm --create /dev/md2 --level=1 --raid-devices=2 missing /dev/sdb3
Check the result with:
cat /proc/mdstat
Create the file-systems on the new RAID devices partitions.
mkfs.ext4 /dev/md0 mkfs.ext4 /dev/md1 mkswap /dev/md2
Now we need to Manually replicate the existing data on existing /dev/sda partitions to new software RAID partitions.
Mount both / and /boot
mount /dev/md0 /mnt/boot/ mount /dev/md1 /mnt/
Copy Existing data using rsync command
rsync -auxHAXSv --exclude=/dev/* --exclude=/proc/* --exclude=/sys/* --exclude=/tmp/* --exclude=/mnt/* /* /mnt
During rsync we got error like below
rsync: rsync_xal_set: lremovexattr(""/mnt/mnt"","security.selinux") failed: Permission denied (13) rsync: rsync_xal_set: lremovexattr(""/mnt/run/initramfs"","security.selinux") failed: Permission denied (13) rsync: rsync_xal_set: lremovexattr(""/mnt/run/initramfs/rwtab"","security.selinux") failed: Permission denied (13) rsync: rsync_xal_set: lremovexattr(""/mnt/run/initramfs/log"","security.selinux") failed: Permission denied (13) rsync: rsync_xal_set: lremovexattr(""/mnt/run/initramfs/state"","security.selinux") failed: Permission denied (13) rsync: rsync_xal_set: lremovexattr(""/mnt/run/initramfs/state/etc"","security.selinux") failed: Permission denied (13) rsync: rsync_xal_set: lremovexattr(""/mnt/run/initramfs/state/etc/sysconfig"","security.selinux") failed: Permission denied (13) rsync: rsync_xal_set: lremovexattr(""/mnt/run/initramfs/state/etc/sysconfig/network-scripts"","security.selinux") failed: Permission denied (13) rsync: rsync_xal_set: lremovexattr(""/mnt/run/initramfs/state/var"","security.selinux") failed: Permission denied (13) rsync: rsync_xal_set: lremovexattr(""/mnt/run/initramfs/state/var/lib"","security.selinux") failed: Permission denied (13) rsync: rsync_xal_set: lremovexattr(""/mnt/run/initramfs/state/var/lib/dhclient"","security.selinux") failed: Permission denied (13) run/user/0/ rsync: rsync_xal_set: lremovexattr(""/mnt/run/user/0"","security.selinux") failed: Permission denied (13)Noticed similar errors reported as bug
https://bugzilla.redhat.com/show_bug.cgi?id=873467
What I understood is the error status rsync command is trying to synchronize the attributes on destination partition to match to attributes on the source partition by removing "extra" attributes. But rsync command has no privilege to perform it even if we run it as root user.
In my case the permission denied are for files inside /run folder. In my understanding /run/ is often implemented as a tmpfs ( mount | fgrep run ) and data in those directories won't survive a reboot (which is a good thing). Which means /run include as a temporary filesystem (tmpfs) which stores volatile runtime data.
So I ignored the rsync errors and proceed with the next steps.
Now mount System information
mount --bind /proc /mnt/proc mount --bind /dev /mnt/dev mount --bind /sys /mnt/sys mount --bind /run /mnt/run
Chroot into /mnt partition for /dev/sdb disk
chroot /mnt/
Edit fstab with new drive UUID information
blkid /dev/md*
/dev/md0: UUID="bdf72caa-716c-431d-ab23-4699feb14bdf" TYPE="ext4″
/dev/md1: UUID="cef39ac1-e53b-4a25-9608-7baf20fade02″ TYPE="ext4″
/dev/md2: UUID="45b6e2b2-cd79-4fdd-8288-80e1db0da874″ TYPE="swap"
Now Open /etc/fstab file and add entries like below.
vim /etc/fstab UUID=your-UUID / ext4 defaults 1 1 UUID=your-UUID /boot ext4 defaults 1 2 UUID=your-UUID swap swap defaults 0 0
Now create a mdadm.conf from current RAID configuration:
mdadm --detail --scan > /etc/mdadm.conf
Backup,Update the current initrd and rebuild the initramfs with the new mdadm.conf:
cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.bck dracut --mdadmconf --fstab --add="mdraid" --filesystems "xfs ext4 ext3" --add-drivers="raid1" --force /boot/initramfs-$(uname -r).img $(uname -r) -M
Now edit grub and add some default parameters to grub.
vim /etc/default/grub GRUB_CMDLINE_LINUX="crashkernel=auto rd.auto rd.auto=1 rhgb quiet" GRUB_PRELOAD_MODULES="mdraid1x"
Make new grub config
grub2-mkconfig -o /boot/grub2/grub.cfg
Install grub on new disk /dev/sdb
grub2-install /dev/sdb
At this point we are going to reboot the system choosing new disk /dev/sdb from bios. Ff all worked out system
will boot with new disk /dev/sdb. After that check mount points and raid status using below commands.
swapon -s mount -t ext4 cat /proc/mdstat
In our case, we switched the disk ports so after reboot new disk become /dev/sda and old disk become /dev/sdb.
So don't get confuse with the screenshot results, if you opted to boot from new disk from bios instead of disk
port swap, in that case the mdstat command results will show the new disk as /dev/sdb itself.
Now we need add old disk to the raid array. So Change partition type to "Linux raid autodetect" for old disk.
fdisk /dev/sdb use "t" to convert all 3 partitions to "fd" (in our case its sdb)
Now Add old disk to raid 1 array. (In our case its sdb)
mdadm --manage /dev/md0 --add /dev/sdb1 mdadm --manage /dev/md1 --add /dev/sdb2 mdadm --manage /dev/md2 --add /dev/sdb3
Check rebuild status using below command and see if it running.
watch -n1 "cat /proc/mdstat"
Reinstall grub on old disk ( In our case its /dev/sdb)
grub2-istall /dev/sdb
This concluded the raid1 setup on existing centos 7.4 install. Once the rebuild completed, the mdstat result will show like below and from that we can confirm its completed and running fine. Try to reboot it again and see if there any issues encountering.
Tiruchirappalli Sivashanmugam